Graham although I can't be certain of a 153, back when ATW▸ or their predecessors ran a Cardiff to Paddington late night after FGW▸ withdrew the late Cardiff Paddington service,they used DMUs▸ normally 158s but on some occasions other units found their way on in place of 158. There was a report of a pacer one night.
I believe 153s
did make it to Paddington occasionally on the old Wales & West services, working in multiple with 158s.
Pacers have certainly got as far as Reading (once, infamously, all the way from Pembroke Dock), and yes, there are rumours of one once having reached Paddington on the
W&W▸ service in 1999, but who knows how true that is...