The P8 doesn’t feature at all in the Maritime and Coastguard Agency‘s next contract (2024+) assumptions. It was specifically excluded during their industry day briefing in May.
All of which makes sense. Civilian SAR around the UK is the responsibility of the Department of Transport. If the DoT wanted to use a P-8A for such purposes they would have to request it from the MoD. The ac does have a JPR role, I.e. military only SAR.