This is always said after the clocks are put back. I don't see it that way at all.
I usually wake up during BST at around 0600. So on Sunday, it will be 0500 GMT. I will be awake, so no 'lying in'. However, come evening I will have to stay up an hour longer.
It won't of course be quite like that. I often go to bed at around 2100 BST, so on Sunday it will be 2000 GMT. I might miss the Mexico Grand Prix (yawn!) as I have seen conflicting start times indicated as being 1900 GMT or 2000 GMT. I think it's the latter.
Jack