How exactly has the LL shown that?!
He's 'playing perfectly fair' to use your own stupid parlance. He's issuing due notice on a rental contract that has a break. That is his legal right to exercise, to repossess his property that he's paid good money to own, rent & maintain over the years.
The OP has since changed her story (anyone else notice this hey!?), she can't afford to buy the house at the market price she thinks it's worth right now, but may be in 4/5 months time, maybe, possibly......
Hmmm, he got it valued over 12 months ago at 350k, so estimate house inflation at 5% in Brexit land (it was 11% in Ireland btw, go figure , so rounding it up ithe house likely to achieve ~370k on the open market in it's current state. (Unoccupied)
He may be handy at DIY & work supervision and figure a few jobs, new carpets & paint throughout and possibly a kitchen renewal & a bit of staging, and he can maybe realise £410-420k.
So, the OP wishes for him to sell to her at 350k in 4/5 months when she may be able to afford that. And any issues with the sale, section form process (she has already admitted considering outstaying her lease, & hinted at becoming a real nuisance, etc, etc). It will be his problem. Yeah right OP, you expect your LL to do without 50-60k extra on the promise of you being maybe able to afford the lower price in 4-5 months.
If I were him now reading this, I'd just want you out ASAP tbh. You're potential trouble for him now & he may well know it.
P.s. Good luck OP, but act fair & don't act the maggot I.e. if you truly want the house, offer what you think it's worth & make your best offer to him. And then respect his decision thereafter on this. It was always his house & he's entitled to do whatever he likes with it within the law. Respect that at least!