iMessages not sending or receiving

Hi,

I use an iPhone 4 and an iPod Touch 4G to chat to my girlfriend who has a 4S and also a 3GS on seperate UK carriers, over the iMessages network. Since we started using iMessages late in 2011, it has been excellent, with messages and Face Time working really well. But things have really deteriorated over the last 24 hours; my messages have said delivered, but she hasn't received them; or she may receive a lot of them at once, if at all. Now I am unable to get 'delivered' messages when I send iMessages.

I am online, using the same connection I am sending this post on, and we are able to message using SMS.

It seems ridiculous, as the Messages app says they're being delivered but they aren't. Any thoughts?

Darren