Like other publicly funded national museums in the United Kingdom, the Science Museum does not charge visitors for admission, although visitors are requested to make a donation if they are able. Temporary exhibitions may incur an admission fee. It is one of the five museums in the Science Museum Group . - more at Wikipedia
very nice, I was there several times and have a huge collection of pictures of it, I've taken my kids and friends who visit, there is always something interesting to see even having been there before.