Just to add to the fun, there is a reduced Liz line service to Heathrow on Sunday 18 March....
I would defintely be wary of the traffic impact during the first weekend. Here in the east end we've had a series of weekend closures of the Blackwall Tunnel. The first couple of weekends when this happened, despite lots of publicity, the roads around the tunnel were in total gridlock. It was mayhem. Seemingly a lot of folk just don't look at warning signs. We're still getting occasional weekend closures but the impact is much less now - seems that folk now check in advance and adapt.