Ok, thinking about a possible ordinary sequence of events... i know about the UK 'Fiance Visa', and of course the Spouse visa for those already married. But what would be the official reaction of the UKBA to a UK citizen marrying a Thai who had entered the UK on an 'Unmarried Partner' visa for 30 months, and then during that time, deciding to get married in a 'normal' way because everything was going fine ? No trickery involved, just 'life'. Would that scenario break some rule that amounts to the UKBA saying 'You shall not marry in the UK at any time without our permission' ? Anyone actually been through this exact process ? Thanks in advance.

Start here: https://www.gov.uk/marriages-civil-partnerships/overview and follow it through, the actual marriage should not be a problem but you need to use specific registry offices.

Thanks RabC - a useful link into the UKBA maze. But as usual with questions that don't fall right into the same old middle-ground of topics with well-known answers, i'm no wiser as to my specific queries. And no, i couldn't find the answers anywhere on the UKBA site. I've written to them... but i really hoped there would be someone on here who had actually gone through what i described, or at least knew about someone who had.

To answer your question in the topic title; nothing.

From Completing application form SET(M)

If we gave you permission to remain in the UK as an unmarried or same-sex partner and are now applying to settle here as the husband, wife or civil partner of the same person, your 2-year qualifying period started on whichever is the later of these two dates:
the date when we gave you permission to remain as an unmarried or same-sex partner; or
the date when you arrived in the UK.

Which shows there is no problem entering as an unmarried partner and then marrying before ILR is granted.

As do questions 2.14 to 2.20 on form SET(M)

Edit:-

You'll notice that the guidance and form linked to are for applications made under the old rules; as it will be at least another 4 years before anyone applies for ILR under the new rules they have not published guidance on this yet.

From your mention of applying, presumably for FLR, after 30 months in the UK I assume that your partner either has not applied yet or applied under the new rules.

However, the principle is the same. There is no problem with entering the UK as an unmarried partner and then marrying before ILR or FLR is applied for or granted. Simply tell them in the application that you have done so.

Edited August 23, 201312 yr by 7by7

Marry in LOS, not UK.

Many thanks 7 by 7 - i will follow that link and read carefully, as i don't really understand the paragraph you provided. Also, we would not be in the position described - as applying AFTER 'leave to remain' had been granted - but rather after being in the UK having been granted Entry Clearance, i.e. in the first 30 months. The UKBA texts usually baffle me - in the paragraph you provide -

If we gave you permission to remain in the UK as an unmarried or same-sex partner and are now applying to settle here as the husband, wife or civil partner of the same person, your 2-year qualifying period started on whichever is the later of these two dates: the date when we gave you permission to remain as an unmarried or same-sex partner; or the date when you arrived in the UK.

I just don't get it - how can 'the date when you arrived in the UK' ever be the later of the two dates ? Surely the date 'when we gave you permission to remain' , would always be the later date ? Or am i being spectacularly dim this morning ? Wouldn't 'permission to remain' always come 30 months after 'permission to enter' (Entry Clearance) I think the paragraph is a muddle.

Also, by beginning with : "If we gave you permission to remain..." the paragraph doesn't actually apply to our possible situation of getting married during the first 30 Months in the UK.

I have emailed the UKBA - not always a successful venture i know - if they answer i will post it here for everyone's benefit.

Edited August 24, 201312 yr by lookingeast

The wording of the official guidance can at times seem confusing. Sometimes because it's written in bureaucratic language, sometimes because they are trying to cover all eventualities, as in this case.

But the upshot is that the answer to your question "What could go wrong with marrying in the UK on an 'Unmarried Partner' visa ?" is; nothing.