You might be interested to know that there is a department in Manchester University called CHSTM. Centre for the History of Science, Technology and Medicine. Most of ther students doing MA and PhD degrees in the dept come from a science background, so that wouldn't hold you back. There is a number of students working on aspects to do with the history of computing.
They have some links with the history department at Manchester too.
My undergraduate degree in unrelated to my PhD subject.