Both the gfs and (to a lesser extent) the ECM have pressure building
over the UK from about a week out. Nothing particularly warm on the
850 hpa temps, but as has been pointed out, we're approaching the
equinox and the stronger sun might well produce some reasonable
afternoon temperatures if skies were clear; light winds could further
accentuate the feel of more pleasant conditions.

See if that stays on the charts through today and especially if the
ECM follows the gfs, which has been keener on this scenario over the
last few runs.