This is a noble false widow (Steatoda nobilis), fairly common in the S & SE of England, they do seem to like man made environments. They're typically quite skittish, not aggressive, bites are often the result of the spider being inadvertantly squashed against the skin.
I'd relocate them to avoid the risk of them getting onto seats/seatbelts & getting squashed. They do well on exterior walls, sheds, outbuildings etc. anywhere where there's a nook/cranny they can hide out in.
For balanced info on false widows follow this link:
Thank you for the speedy response - I saw it today but couldn't catch it.... Hopefully I will have more luck tomorow and will feel much happier once it has been re-homed as definitely don't want any of the kids to sit on it or anything. Again thank you ðŸ˜ƒ