The drill: maintain 250kts or less below FL 100 in U.K airspace unless requested to do otherwise by ATC. Of course you can always ask them if you have to maintain a speed restriction.. they may say at your discretion below 300/320 kts etc.
London airspace is essentially the LTMA which is Class A, but plates do specify these restrictions on both SIDs and STARs into and out of major U.K airports. Heathrow's CTA is Class A, but Gatwick, Luton and Stansted's CTA are Class D.
So irrespective of the class of airspace, it would be wise to maintain 250kts or less below FL100. Indeed, there may be times when ATC request your assistance and ask you if you can maintain a high speed say 300kts until otherwise cleared. I do believe EasyJet have a company policy of 250kts or less below FL100 regardless of requests.. Ryanair trying to get in fast again where they, some things never change
Keep Safe
74 Downwind
