Not sure I follow. If I order a M3LR now at today’s price on the website then If Tesla up prices in between order and delivery surely they honour the order price? Is that what you’re saying or not?
I ordered at X price
Tesla reduced price to Y
I paid Y
If Tesla had raised price to Z, I would have paid X
No idea where Tesla prices in GBP are heading. They've gone up in USD over the year & recently. Tesla have lots of demand, chips & materials are up. China make lots (all?) UK cars, so scope to make cheaper. You get the SMALLER price of the 2 unless you change spec.
Anyway, not much point haggling with Tesla as they are supply, not demand limited at the moment (and next few years in my opinion). Also, they're not dealerships trying to flog you waxed seats & zimmerit anti-rust treatments for underbodies (or whatever they try to do to bump up the price).
Tesla is straight-forward. Choose car model (effectively only 3 in UK at the moment, AFAIK), spec (SR+, LR or Performance) and colour (free white, for now). No haggling unless it's a demo or inventory just before quarter close (others might know better).
I'm biased, but I like the Long Range by the way. SR+ would be fine for me, but I like the extra range. Performance would worry me too much with the potholes I see. Having some extra rubber to absorb the bumps helps range, survive potholes, more comfort for passengers. I also think that the Performance brakes are best left to the track, but haven't direct experience.
Whichever one you get, I hope (and expect) you'll love it. Get well soon.