Your MPLS contract is up for renewal. The provider has come back with a quote — slightly higher than last time, even though your bandwidth requirements haven't changed dramatically. Someone on the team has mentioned SD-WAN, a colleague forwarded an article about it, and now you need to make a decision. Renew the MPLS, migrate to SD-WAN, or some combination of both.

This is the decision context for most UK SMB IT managers in 2026. MPLS is mature, understood, and trusted — but it's expensive relative to what commodity broadband and internet-based overlays can now deliver. SD-WAN has moved well past the hype phase; it's deployed at scale in enterprises and is increasingly viable for businesses with five sites or fewer. This post works through the practical trade-offs.

WHAT MPLS GIVES YOU (AND WHAT IT COSTS)

MPLS (Multiprotocol Label Switching) is a private circuit technology. Your traffic travels across the carrier's own network — not the public internet — from your sites to a hub point or between branches. That private path is the reason MPLS has been the default choice for enterprise WAN connectivity for two decades.

The tangible benefits are real. MPLS delivers guaranteed QoS end-to-end across a carrier-managed path. Jitter and latency are predictable because your traffic is not competing with general internet traffic on the carrier's backbone. The SLA is contractual — your provider (BT, Virgin Media Business, Colt, or their wholesale equivalents) commits to uptime, latency, and repair times in ways that a commodity broadband product does not.

But the cost model is punishing. MPLS is priced per-Mbps at rates that dwarf commodity broadband. A 100Mbps MPLS circuit from a major UK carrier will cost substantially more per month than a 1Gbps dedicated internet access line. Bandwidth upgrades require contract renegotiation. New site provisioning involves BT Openreach wayleave processes — which in practice can mean six to twelve weeks before you have a live circuit, particularly for sites in buildings without existing Openreach infrastructure. You are also tied to the carrier's network edge; migrating providers means re-provisioning every site.

The UK-specific reality: most MPLS contracts run 3–5 years. By the time you hit renewal, the bandwidth you're paying a premium for is less impressive than it was when you signed. The competitive broadband landscape has moved on substantially in five years; your MPLS pricing often hasn't moved with it.

WHAT SD-WAN CHANGES

SD-WAN is an overlay technology. It runs on top of whatever underlay circuits you have — commodity ADSL, FTTC, FTTP, 4G/5G, or a dedicated internet access (DIA) line — and provides the intelligence layer: path selection, application-aware routing, failover, and centralised policy management.

The cost per megabit drops dramatically. A site that previously had a 10Mbps MPLS circuit costing £800/month can be served by a 100Mbps FTTP line at a fraction of that cost, with an SD-WAN appliance providing the QoS and resilience logic that MPLS previously handled in the carrier network.

FortiGate SD-WAN, for example, provides per-application path selection based on SLA targets. If your VoIP traffic requires sub-20ms latency, you configure a health check and SLA policy: route VoIP over whichever WAN link meets the target, fail over to the secondary link if the primary degrades. This logic happens in the SD-WAN appliance at your site, not in the carrier's network.

The performance caveat is real though: SD-WAN QoS depends on underlay quality. You are building intelligence on top of commodity broadband, which means the underlying broadband contention and jitter characteristics still matter. For voice and video — Microsoft Teams, hosted telephony — you need to be confident that your internet circuits can sustain the SLA targets your SD-WAN policy requires. In dense urban areas with good FTTP availability, this is generally manageable. In areas with limited broadband infrastructure, it's a constraint worth modelling before you commit to a migration.

WHEN MPLS STILL WINS

MPLS is not a failed technology. There are specific scenarios where it remains the right choice:

  • Ultra-low latency requirements — financial trading, real-time industrial control systems, or applications with strict sub-5ms latency requirements between sites. SD-WAN over commodity broadband cannot reliably guarantee this. MPLS with a contractual latency SLA can
  • Regulated environments with circuit isolation mandates — some compliance frameworks or contractual arrangements require proof that traffic travels exclusively on a private network. MPLS satisfies this; internet-based SD-WAN technically does not, even with encryption
  • Rural sites with no viable broadband alternative — if your site is in a location where the only available broadband is low-speed ADSL or 4G with poor coverage, MPLS may be the only way to guarantee the bandwidth and reliability you need
  • Single-site businesses — if you have one office connecting to a hosted data centre, the complexity of SD-WAN deployment may not be justified. A single DIA line with a capable firewall handles most single-site requirements adequately

WHEN SD-WAN IS THE RIGHT MOVE

SD-WAN makes sense in most modern multi-site environments, particularly where:

  • You have multiple sites with mixed connectivity — one site has FTTP, another has FTTC, a third has 4G backup. SD-WAN manages all of these through a consistent policy layer, selecting the best path per application and failing over automatically
  • Cost reduction is a priority — replacing MPLS with commodity broadband plus SD-WAN typically delivers 40–70% WAN cost savings. The SD-WAN appliance cost is recovered quickly
  • You've migrated to cloud-first applications — if your traffic is predominantly Microsoft 365, Teams, Salesforce, or other SaaS, routing it all back through an MPLS hub to reach the internet is actively harmful to performance. SD-WAN with direct internet breakout at each site reduces latency for cloud applications substantially
  • Rapid site deployment is important — a new SD-WAN site can be provisioned on an existing FTTC or FTTP line in a day. An MPLS circuit for the same site means weeks of Openreach provision lead time
  • You want to retain MPLS for critical traffic — the hybrid model works well. Run SD-WAN across all sites with commodity internet as the primary underlay, and keep a single MPLS or private circuit for traffic that genuinely requires guaranteed QoS. Use SD-WAN to steer that traffic onto the MPLS member automatically

HOW TO DECIDE

Run through these questions for your specific environment:

  • What is your current MPLS cost per site per month? — Compare against a realistic FTTP or DIA quote for the same sites plus SD-WAN appliance amortised over three years
  • What applications are most sensitive to latency and jitter? — VoIP and real-time video are the most demanding. If these are cloud-hosted (Teams Phone, RingCentral), SD-WAN with good internet circuits typically handles them. If they're on-premise with strict SLAs, model carefully
  • How many sites need to connect? — SD-WAN economics improve with site count. Two sites: marginal. Ten sites: compelling
  • What broadband is available at each site? — FTTP availability is the key variable in the UK. Check Openreach and Virgin Media Business coverage for each postcode before committing to a SD-WAN migration
  • Do you have in-house expertise to manage SD-WAN policy? — SD-WAN adds operational complexity. If your team is comfortable managing firewall policies, SD-WAN policy is manageable. If your WAN is currently fire-and-forget MPLS, factor in the management overhead
  • When does your current MPLS contract expire? — If you're mid-contract, a migration needs to be costed including early termination charges. If you're at renewal, now is the time to act

NEED HELP EVALUATING YOUR WAN OPTIONS?

We help UK businesses evaluate and deploy SD-WAN solutions — including FortiGate SD-WAN, circuit selection, and migration planning. See our connectivity and SD-WAN services or get in touch to discuss your setup.