I'd do A66 to Scotch Corner, A1/A1(M) down to the A14 split at Alconbury then A14, M11 to A406 (Watch out for the 50mph sign about 2 miles from the end of the M11. The camera 200 yds after it is the highest earning speed camera in the UK!). So, go left onto the A406. Stay in the left lane and come off at the Redbridge R'about and go nearly all the way round down the A12, through Blackwall Tunnel and onto the A102(M), which becomes the A2. After about 3 or 4 miles you will come to the A205 South Circular Junc. Down the slip and turn right and just follow the A205 toward Catford. Go over 2 big r'abouts and up the hill to a set of traffic lights. Turn left on the A2212 toward Bromley. When you get to the Bromley one way system go right toward Beckenham on the A222. Its a bit convaluted, but takes you clear of the Catford one way system which is worse!! Safe journey.