Krallu
If you maintain 1,000 feet above the highest obstacle within 5nm of your track then in the London area your MSA is approx 1750amsl
So a pragmatic and sensible personal SE cloud limit might be 1000 foot agl, this will provide some level of VFR in the last couple of minutes for finding a landing field. Unfortunately you may still hit a tall mast during descent whilst IMC unless you know where you are in relation to the masts.
Must emphasise that this is a suggested personal limit based on a specific area, if near high ground then you might need to wait for 500 ceiling (or higher) above high ground prior to flight (i.e. ensuring no cloud on hills).
Most mountain training recommends 2000 clearance above the ridges of high ground if wind is in excess of 20Knots so it is not just about clouds but also turbulence.