Don't know about civil service, with the way they're cutting back it's not the job for life that people assume it will be.

There are part time options for doing PGcert, have a look at:
www.uce.ac.uk/web2/education/earlyyears.html.

Have a look at Newman College too, last year PGCE students didn't have to pay fees and were eligible for training salaries of 6K, not much but better than nothing!
http://www.newman.ac.uk/for_prospective_students/

With your background in computing, you could look at teaching jobs in IT at university level. I don't know the specifics of what you do but commercial experience is always valuable, the academic stuff can be picked up later. You don't always need a teaching qualification at uni level, as lecturers are given the opportunity to obtain the necessary quals while they're working. I did a Cert Ed, which is part of an MA in education, not the same as a PGCert but still well regarded. The course was paid for by my employers and I was given time in my working week to do it. Teaching at uni level is not as scary as teaching schoolkids! Of course, whatever you do you need to feel ready. However, if you're not enjoying the job any more it may be time to move on.