//they've got to be taking the pi$$//
umm, no actually. the track was relayed over the weekend, and whilst it settles down the rails were stressed in accord with temperatures usually prevailing, with final stressing applied later. this would be sufficient to permit the new but unfettled track to be used at less than normal speed, but higher than the 20mph that might usually apply after such relaying work.
the unusually high temperatures mean that the stressing applied wasn't sufficient, rendering the rails likely to buckle in direct sunlight. hence the speed restriction of 20mph.