Rhiannon, I too say Thameslink, but should you want to drive, here's the route that I, personally, would take. I know the London/Cambridge stretch of the M11 quite well - used to use it lots. Hasn't the London bit, where it joins the A406, been improved - it's so much quicker now.
Get onto the M11. Do NOT turn off at Junction 27, where it joins the M25, this will take you miles out of your way.
Stay on the M11 until you hit the A406 - the good old North Circular. It is well signposted. You want to head East.
You are heading towards the Millenium Dome and the Blackwall Tunnel (not to be confused, ever, ever, ever, with the Dartford Crossing). Follow the signs to the Millenium Dome - by now there should be lots of them. You will find ample parking right next to the Dome and its high tech tube station. It costs £4.00 for a days parking. Then hop on a train - they run every few minutes, and in less than 10 minutes you will be at London Bridge station.
As it happens, I may be heading up north on the M11 this weekend. On my way back, I'll check that Millenium Dome signs are still up.
If you are hell bent on driving right up to Vinopolis, I can give you an alternative, but pretty long, route.