Do not be tempted into buying hot dogs or burgers from any of the street vendors that plague the West End of London.
They are unlicensed and therefore unregulated and the standards of food preparation and hygeine would, quite frankly, make your hair stand on end. I know a number of people who have become very ill after eating from these stalls.
There are plenty of proper eating places in town, open all hours, and you really should have no need to resort to using these vendors.
As a side issue, most of the vendors are controlled by Eastern European criminal "Gang Bosses" (and treated pretty appallingly by them) so not only are you running the risk of serious illness, you are also supporting organised criminal activity.
When you are in central London you will come across a number of food stalls, which sell hamburgers, hotdogs etc. BEWARE, they are very expensive and unhealthy. There have been a number of television investigations into these food stalls, which have shown them to be about as healthy as eating a dead pigeon. The meat is old and the food is often re-heated day after day if it is not sold. My advice is for you to stick to McDonalds!
You may see them at major tourist attractions or in the parks
Don't eat anything from either you don't know where they've been or how long they've been there. No-one i know who lives in london would ever buy anything from either of them. I bought a bottle of water from an ice-cream van at Tate modern and it was two months out of date and the label was in Turkish!
Although I did not eat any of the food in many of the parks that we visited, we did see the occassional food vendor.
All the food that I saw seemed to be prepared pretty well, but it appears that London may have a few issues with the quality of the food that these vendors serve.
I was interested to read this notice on the store front of a neighboring shop mentioning that it may not be the best to eat their food.
You should be fine... but I still wanted to warn you!
Just a wee bit of a problem for us yanks, seems as though most of the pubs have great beer and even the fish & chips are decent, but the tartar sauce is served warm and it could be off. I should have asked how long ago the tartar sauce was made, or perhaps just used a squeeze of lemon. I spent a full day, recovering.
When eating anything warm, make sure that it is freshly made. Ask before eating is a good rule of thumb. If you feel something should be cold, check the temp. out before eating. If you would like to eat English cookery but want to make it yourself, the website below is a great recipe finder from the English Kitchen, with music to keep you company.
I honestly don't recommend that you eat food such as burgers and hotdogs from the illegal trolley stands on the streets as they have very poor hygiene standards. However, this rule is ignored by everyone coming home from a long evening at the pub, when nothing will satisfy that hunger like the traditional "dirty burger"!
Please do go to the Tower of London, however, DO NOT under any circumstances eat the "Fish and chips" meal at the "Digby Trout" restaurant inside the Tower. The fish was off (old) and the chips weren't cooked thoroughly. We both got sick for the wonderful price of: 17 pounds and 90 pence (£17.90 = $32.04) for 2 meals and 2 drinks.
Do not buy from unlicensed Food vendors, You coud see the license presented, or ask them. It is very dangerous to purchase hot/cold food from unlicensed vendors, as it can be contaminated.
If you want to be safe, just eat from the worldwide franchises such as Mcdonalds, KFC, Burger King etc.
But expect high prices, there has been a considerable amount of inflation, over the years. Better safe than Sorry