A backup mobile connection is useful when your train enters a signal dead zone. It becomes considerably more interesting when you can take the same data allowance on a weekend in Paris without buying another eSIM.

That is the change Keep On Roaming has made to Sidekick. Since 18 September 2026, the UK-focused backup eSIM has included data roaming across the EU, EEA and Switzerland at no extra cost. Customers can use their full monthly allowance in those destinations rather than paying for a separate European bundle. The addition turns a domestic coverage safeguard into a more versatile travel companion.

One eSIM, two jobs

Sidekick was built to sit alongside your existing UK mobile plan, not replace your usual number. In the UK, it can access EE, O2, Vodafone and Three, selecting an available network when your primary provider leaves you without usable data. The idea is straightforward: a second route online when your first one fails.

READ MORE: eSIM and Regular SIM: Can You Use Both At the Same Time?

That matters because national coverage figures hide local gaps. Ofcom’s spring 2026 update estimated good outdoor 4G coverage across 96% of UK landmass from at least one network, but only 84% from all four. The difference explains why a phone can lose service in a particular spot even when someone standing next to you has a connection on another provider.

Sidekick does not create signal where none exists, nor should its multi-network access be confused with uninterrupted service in every location. Switching between the phone’s main line and backup data line can also depend on device settings. And because Sidekick is positioned as a data backup, users should not assume it restores ordinary calls or SMS on their main number when that network is unavailable.

What changed for travellers

Previously, Sidekick’s main selling point stopped at the UK border. Now its existing allowance works in every EU and EEA country, plus Switzerland. The EEA coverage includes Norway, Iceland and Liechtenstein; Switzerland is a separate, welcome addition rather than an EU member.

READ MORE: EU’s Next Roaming Regulation: What It Means for eSIM Users and Telcos

Keep On Roaming says the roaming is included “at no extra cost”. For someone who needs backup connectivity on a UK commute and takes occasional European trips, that means one subscription can serve both situations. Abroad, the eSIM connects to local partner networks; it does not somehow carry the four UK networks overseas.

There is an important boundary. Keep On Roaming describes Sidekick as a UK product with roaming intended for periodic travel, not permanent use abroad. The published plan page does not spell out a precise long-stay threshold in its overview, so extended-stay users should check the applicable terms before relying on it. Nor does EU, EEA and Swiss coverage mean all of geographical Europe: check destinations such as Turkey, Monaco and Andorra separately.

What the plans actually cost

The data amounts have not changed with the roaming announcement. Sidekick currently advertises three monthly allowances, each with a 30-day free trial and a choice between annual billing and a rolling monthly plan:

Those headline annual rates are not monthly payments: the full 12-month price is billed upfront. The provider also advertises the ability to cancel, but customers choosing the annual option should check renewal and refund terms rather than treating it as financially identical to a rolling subscription.

READ MORE: The 10–20GB Sweet Spot: Where Smart Travelers Actually Spend

For light backup use, 5GB may cover maps, messaging and occasional hotspot sessions. Anyone using the backup line heavily, or relying on it for video calls while travelling, will need to think more carefully about monthly consumption. UK and European usage draw from the same allowance, so data spent at home is not magically replenished at the airport.

A different kind of travel eSIM

This launch is interesting because it challenges a familiar division in the eSIM market. Travel eSIMs are usually bought for a destination and a trip; domestic multi-network products are sold as protection against coverage gaps. Sidekick is trying to make that second category useful between trips as well.

It is not alone. Fuse Mobile offers access to all four UK networks, with its 10GB Pulse and 15GB Surge plans including roaming in more than 120 countries. Its rolling prices are £9.99 and £14.99 respectively, giving travellers a broader geographic footprint but different data allowances to compare. Anywhere eSIM, another UK backup option, explicitly describes its product as UK-only; its offer also includes calls and texts, which makes a like-for-like comparison with data-focused Sidekick difficult.

READ MORE: When a Local SIM Is Actually Worse Than a Travel eSIM

The shift is relevant beyond any single provider. A subscriber who already pays for resilient connectivity at home may be less inclined to buy a separate short-trip eSIM. Equally, someone who travels outside Sidekick’s included area, needs a local number or spends most of the year abroad may still be better served by a dedicated travel plan or a suitable primary mobile package.

Conclusion

The real competitive question is no longer simply how many networks an eSIM can reach. It is how much everyday friction one subscription can remove. Sidekick’s European roaming gives a backup plan a second reason to exist, without asking customers to install and manage another product every time they travel.

But the next differentiator will be clarity: transparent long-stay rules, straightforward annual billing terms, and a plain explanation of how backup data behaves across different phones. Providers that make those details as easy to understand as their coverage maps will give travellers something more valuable than a longer destination list: confidence that the connection they bought will work in the situations they actually face.