Can you travel while a UK visa or ILR application is pending?

The rules below apply to an application made from inside the UK to extend, switch or settle — a visa extension, a change of route, or indefinite leave to remain. They are all "applications for permission to stay", which is the category the Immigration Rules use.

They do not apply to:

• Visiting the UK. A Standard Visitor is admitted for up to 6 months per visit and generally cannot switch to another route from inside the UK, so none of this arises. If you are here as a tourist or on a business visit, your question is the per-visit limit, not an extension.
• Citizenship (naturalisation), which is not an application to vary permission. You would be travelling on the ILR or status you already hold.
• Applications made from abroad, where there is no UK permission to extend in the first place.

When you apply before your current permission expires and the Home Office has not yet decided, your existing permission continues automatically until it does. It also continues while an appeal or administrative review you are entitled to is pending. In law this comes from section 3C of the Immigration Act 1971, which is why advisers call it "3C leave" — but the mechanism is the useful part, not the name.

Its purpose is narrow: it stops someone who applied on time from becoming an overstayer because of Home Office processing time. It is cover for a gap, not a grant of new rights.

Two limits follow from that, and both catch people out:

• It only covers in-time applications. Apply after your permission has already expired and there is nothing to extend.
• It ends if you leave the UK. The Home Office guidance says so expressly.

So if your visa has expired and this extension is the only thing keeping you lawful, boarding a flight removes it. You are then abroad without valid permission, and coming back requires permission you no longer hold.

There is a second consequence, and it is triggered by a wider boundary than the first.

Under paragraph 34K of the Immigration Rules, an application for permission to stay is treated as withdrawn on the date you leave the Common Travel Area — automatically, not at a caseworker's discretion. The automatic extension, by contrast, lapses when you leave the UK.

The two do not line up, which produces a distinction worth knowing:

• A trip to Ireland ends the extension keeping you lawful, but does not withdraw the application.
• A trip anywhere else does both.

Neither is a good outcome, and because the consequences are status-level rather than administrative, this is a point to take advice on your own circumstances before booking — not to reason from a forum post about someone else's route.

• GOV.UK — 3C and 3D leave: caseworker guidance
• Immigration Act 1971, section 3C
• GOV.UK — Immigration Rules, Appendix Continuous Residence
• GOV.UK — Immigration Rules Part 1, paragraph 34K (withdrawal)