ah bluebread, can give you several places to go
come into central London on the A40, over the marylebone flyover and carry on going straight. Past Baker Street Tube, Past Regent's park tube. Keep going but stay in the left lane (not the bus lane, the one next to that).
once you go past regent's park, I think there's a left only turn. STRAIGHT after the left only turn, there's a sign to filter off left for Holborn and the West End (with a road name, can't remember which one, probably A400 West End something like that).
You'll know where it is because it means you DON'T go into the Euston underpass. The filter left is JUST before this. If you're in the underpass, you've gone too far (doesn't matter, you can get back again if necessary, just gets a bit complicated).
You go off that filter.
Stay in the right hand lane and turn right and as you turn right, you follow the traffic (it will take you right then left a bit so you are parallel with the main road).
Then you hit a traffic light and you go straight through (it takes you to the right).
(the road you are on now is Gower Street, A400).
Turn left on Kempel Street (the next left turn after Torrington Street).
Turn right at the end and follow the road round to the left (Montague Pl).
Turn left into Russell Square. Go round the square and at the traffic lights at the end, get in the lane to turn left.
Turn left onto Southampton Row/Woburn Place (big road)
Turn first right into Coram Street. Parking lot on your right and it's £19 for the day.
Loads of buses around there to get you into where you need to go.
Also ludicrously convenient for getting home. You come out of the parking lot. Turn right onto Southampton Row and then left at the end and you're on the Marylebone Rd and you keep going straight straight and that's the A40.
Anyway, you can probably ignore all those directions if you have a satnav and just type in Coram Street