Thanks for the options!
its a long and slightly painful story - which involves being let down by the person who was going to give us a lift to Heathrow - they then ended up insisting on buying us HEX tickets (as they said it was good!) - despite protestations.
Iknow - not ideal at all but it is what it is so we’re making the best of this and we’ll not go down this route again!!
We are in Bexleyheath- but to add to the story the Bexleyheath line is closed this weekend! But we can easily start from another local station - Abbey wood or Belvedere probably (helpful person giving us a lift there)

Next time we’ll just book parking!