I've told them I'm 52kg, weighed myself when I got home and I was 48.6.
Do you know if it's a problem? I will tell them tomorrow but I'm not in the UK and I don't know if I'll get across the right thing with the language barrier. So it would be useful to know if it's really urgent and I need to try everything to explain or whether I can try to say so but ultimately not worry about it.
I am thinking that it can't be too much of a problem because if they needed accuracy, they would have weighed me rather than asking. But at the same time it is almost 10% of my total weight.