I've a vague recollection that the Eastern part is an 'early' aulacogen related to the faulting and rifting in eg North Sea. This would make it a weak-zone for any tectonic stress, be that lateral or extensional...
You'd have to look at the regional stress-field due African plate's sorta-Northward plus clock-wise progress, and second-order stuff due interposed Iberia / Western Europe getting pushed about / rotated...
At least London Basin need not consider Wilson Cycle subduction zones & consequences for near-future, or even several millennia. IMHO, it is not speculation to say such processes are simply too slow. Should Gibraltar shelf spawn an Atlantic-swallowing trench, would take a geological age before that spreads up coast, or down-goings become volcanic up-comings per Caribbean Arc...
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snorkack
2,190
477
Found the answer. London Basin is able to drift east-west. It is the "average" of Earth crustal plates that must not drift east or west.