RAT5,
Or perhaps the lead a/c was a 757, which if followed by any other M in the UK does not require wake turbulence separation. We used to come across that at LHR quite a bit when BA, BMI and Aer Lingus 320/737s would go wheels up behind a 757, but those same types from countries which applied the ICAO '757 is a H if followed by a M on departure' separations used to ask us for/tell us they needed 2 mins.
As has been said, UK applies rotation to rotation, and ATC cannot reduce the minima, even if the pilot wants to do so.