I thought that if your employer turned down your request for flexible working, they had to give really good reasons why?
I don't live in the UK so I don't know how it works in practice; this thread is really interesting.
I live in Spain where part time working is a right for parents with children under 5. However, any Spanish person I have ever asked about this says that yes, that's the law, but in practice you'll find that actually using this law will have a very bad effect on your career. Therefore most Spanish "career" women go back to work when their babies are only 4 months old.
I do work part time and it is great for me - my husband works part time too, so we share looking after our baby. His hours were harder to fit in, so he doesn't do as much as me and I am the main earner - but this isn't really a problem - we are just SO lucky to be able to both spend so much time with our baby and I am very lucky to be able to maintain my career.
I feel very strongly that whenever part time or flexible working is discussed that fathers should take more of an interest and get more involved. There is no reason why fathers shouldn't be looking after their children more, especially after the first 6 weeks. Seems to me that this would solve all sorts of issues - marital strife (misunderstandings), baby missing out on father, women getting overlooked at work because they're seen as a riskier bet than men (due to maternity leave/flexi working)...etc etc....