Thanks everybody for the suggestions.
Humberside is indeed hard to reach by the airlines for me, so I'll check out Cranfield and Elstree. An advantage of Cranfield over Elstree seems to be the available IAPs on-site (RNAV, LOC, ILS) [1], so not much repositioning would necessary.
On the other hand, the goal is to transition to instrument flying in Europe, so maybe I should look more which location has the more challenging instrument approaches closeby ...
By the way, how do you practice instrument flying in the UK? Do you also ask ATC for "practice approaches" (like in the US) and simulate the radio calls but stay VFR; or do you go "real IFR"?
[1]
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