Upvote:4
What if I get a round trip for two weeks and the Immigration officer gives me exactly two weeks stay, is that possible? Or is the minimum they could give six months?
6 months is the default and maximum leave they'll grant a visa-free national. Should they suspect you intend to live in the UK and/or seek employment, they may well grant a shorter leave. To be frank, though, if they aren't convinced of your intentions, more often than not they'll simply refuse you entry.
Personally, to err on the side of caution, if I were you I'd bring any documentation proving your participation in the events (including the one in France), as well a copy of your bank statement, onward flight confirmation to France, employment contract, and anything else proving your purpose for visiting the UK and your intention to return home. Of course, do not present all of this to the IO upfront, but have it to show them if asked.
Unfortunately, you being friends with a British citizen of the opposite sex is very likely to raise a red flag, and you already understand why (if she wasn't British, it would not be as bad). Again, documentation, documentation, documentation, proving every single tie you have to St Lucia, as well as your flight confirmations to France and back home, are a great idea to have.
I also think you should screenshot the Thomas Cook booking page showing fares for different dates and print it out, to be able to prove why you're travelling on your dates. It just might come in handy - you never know.
Furthermore, a letter of invitation from your friend is something I would recommend, stating the duration and motive of your stay, as well as the fact that she will not be financially supporting you (because if she did, it would be a reason for you to stay illegally)
Collect all these documents in an A4 soft binder, so you have them neatly organised. You may also want to include a print-out of section V4 and Appendix 3 of the Rules to refer to if need be.
Last but not least: trying to shy away from explaining to the IO your exact circumstances in accurate detail (like you're doing here on Travelstack), especially with your fairly "high-risk" plans, will lead to you being refused entry and removed. If this happens, you will have a much harder time re-entering without a visa.