Wayne as a Londoner myself (now living in the US) I can tell you that spring is the best time time to go there.
I recommend you stay away from the lager and stick with the good London brews such as Fullers London Pride or Young's Special.
You have had some great input on the thread....overall I agree with Big
Oil, his suggestions are "must haves".
If you are going to Ipswich it will be worth making the extra effort to visit Ely. Its one of the most beautiful cities in England with an ancient cathedral that will astound you.
Oh and by the way its traditional for first time visitors to go up to the first policeman they see and steal their helmet while shouting "all coppers are b@stards!". Extra points if you actually do this at the airport. Its OK, they are all in on the joke.