In message
,
Mizter T writes

it's cheaper the more passengers you have (one adult GBP40, two are
GBP70, three GBP90 and four GBP100). It seems that National Express
don't serve this route at all on Xmas day (has that always been so?),
but I do wonder just how much more expensive a (mini)cab might be,
even on the 25th?

Even reputable mini-cabs charge double on Christmas Day, so expect to
pay around GBP 140 for Heathrow to Gatwick. I think I'd opt for the 847,
unless timing was absolutely critical.
--
Paul Terry