According to the Boeing 737NG Manual, the normal taxi speed limit is 20 kts (23mph) but on long straight taxiways up to 30 kts is permitted (34mph).

Then you have high-speed turn-off taxiways which exit the runway at a lesser angle e.g. 45 degrees and depending on the airport concerned normally permit speeds up to 50 kts (57mph).

However, airline operators and airports may set down their own limitations.

Remember that both DUB and STN have long straight taxiways running parallel to the runway, and if you land on a westerly heading at either airport then it's a long taxi back to the terminal. At Heathrow there are lots of "blocks" of taxiways and crossings where you would have to slow down to allow other traffic to pass.