The UK has actually remained a member of the EU's science funding programme after Brexit as part of the exit deal, although that membership has not been formally ratified yet.
Yes, that is part of the trade and cooperation agreement (who knows how long this thing will last, though?)
It includes mechanisms for the UK to pay if British scientists get too much of EU money. Who can bet anything on the British government keeping their word when they need to pay? The government with no qualms about breaking international laws “in specific and limited ways” when it suits them, and that is reneging on its promises about the Irish protocol?
Besides, this does not cover any use of other EU funds beyond Horizon Europe, like the ERDF.
