I think prudence really depends on the whim of the executive, since generally the executive is Parliament given the majority it normally possesses. A number of British governments have historically shown little regard for the unpredictable consequences of violating international law.

For example, Iraq, the Chagos Islands, the Brexit trade deal concerning customs checks in Northern Ireland, etc.

I suppose it's all really just one big political matter: do they want to chance it? Probably not, but they could, legally. We just haven't had the government who's willing to do that yet, but given the current government's willingness to flout international law, prudence seems like it might have vanished some time ago...