It's a provisional offer of a grant, erm. In the real world it's a nailed on certainty i.e. once you get that second offer letter and buy and licence a new EV before the defined expiry date you're getting your money. However, nobody I spoke with is prepared to commit that to paper. The letter says there's a chance you won't get your money i.e. if funds run out. My OCD won't let me ignore what's written in black and white regardless of the fact that I know that's completely irrational.
You don't need to get the scrappage cert before the specific offer expiry date. All you need to do is buy and licence a new EV, await confirmation that it's approved as being approved having already been specified as approved within the list of approved vehicles enclosed with your provisional offer letter and, on receipt of that confirmation, book your ISI. You can continue using your existing car (whether you're scrapping it or not) until the new car is licenced i.e. passes it's ISI - of course you may have practical difficulties in doing that such as not wanting to buy a new meter or not being able to insure two cars but that's the same whether you're getting a grant or not, I guess. After passing the ISI you get your payment form. At that point the money is in the bank and you can scrap your old car and submit the relevant paperwork pretty much at your leisure but not after 13 December in the case of ESPSV25. None of that is particularly clear from the provisional offer letter - that just says you have to comply with all conditions before the provisional offer lapses. In my case that was "on 09/09/2025 or when there is no longer any amount available under the 2025 Available Funding to be made available as an eSPSV Grant, whichever is earlier".