If HST▸ is at Swindon, possibly platform 1 London bound?
No it would have to be platform 3 otherwise the lights from the County ground would not be visible in the background - which they are
They don't look like proper floodlights do they? The County Ground was equipped with lights early - 1951 - and there are loads of pictures from 1969 (the year Swindon won the League Cup) the show big square modern-looking banks of lights. And anyway, isn't the ground a bit too far from the station for two (or more) lighting mast to be that far apart?
They look more like industrial lighting to me, and quite likely a big goods/marshalling yard. Of course they've all gone now, so I've no idea where that one might have been.
PS: Er, um ... that picture was of Wembley, of course, and I can't find one of the County Ground. But I still don't see a set of (probably) four stadium lights.