:... the reason I'm suggesting dispensing with any formal engagement is because, in my opinion, it's an infinitely more expensive choice. The cost of a *fiancee visa is precisely the same as a Spousal one ... both £550+ ... and then there is the *added expense of handing over this amount [at least] AGAIN to apply for FLR (Further Leave to Remain) if you marry over HERE, as the law, as it stands, only allows her to stay in the UK for a maximum period of six months (within which period, the wedding MUST take place).
That's my advice for what it's worth, mate. Others - for reasons best known to themselves - might disagree. But, if I were you, I'd follow my own instincts
[as I DID, in the end ... once I'd been made well and truly aware that the tourist/visit method (which I'd wanted to begin with) was likely to prove a non-starter]. And I've never regretted it. So, if the pair of you are really serious about one another, then GO, go, go ...