janisj

I agree with heti that there are lots of routes (scenic with lots to see along the way) that avoid the M-25. But having to be at the castle by 2PM makes most of those difficult.

Say they did go to Clandon Park and/or Newlands and say via Tunbridge Wells on to Leeds Castle - that is a 3.5 to 4 hour drive without stops. The straight drive would be fine, but visiting sites along the way messes up the schedule.

(I am still a bit confused about staying in Harrow though)

hetismij2

Maybe they have family in Harrow, it doesn't really matter does it?

M25 assuming it is flowing and it is only an hour to Leeds Castle from LHR. They pick up the car at 9 so have plenty of time for a scenic drive down with maybe a stop at Newlands Corner.
If they take the M25 to the A3 then down to Clandon they still have time to get to Leeds by 14.00 with a couple of hours at Clandon before heading back to the M25 for instance.
Just throwing some ideas out there - they can work out what suits them best using maps and the internet.

janisj

"M25 assuming it is flowing . . ." Sure -- if it's flowing - of the last 6 or 7 times I've driven the southern loop of the M-25 -- only once was the traffic 'flowing'. Just this last May LHR to Sissinghurst with a little over half the journey being on the M-25 -- took more than 2.5 hours (GoogleMap figures that would be a 1hr 15 minute drive)

The OP just needs to be aware that driving through SE England (whether on the M's or smaller local roads) can be really congested. The drive could take 90 minutes -- or 3X that.