If I go to London now I go to Stanmore tube (top of the Jubilee line). If you come down the M1, come off at J4 on to the A41 via the slip road. At the next r'about turn right. Straight over the next r'about and Stanmore tube is about 400 yds on your left. The car park is just before the station entrance and well signposted. 5 minutes after leaving the motorway you will be in the car park. You can then get the Jubilee all the way to Canada Water, which will leave you about a 20 minute walk to the Den.