How long have you been an o2 mobile user, Barmoor? I ask because I've got it free for a year, having had their mobile for ages.
It's worth a try and they told me to ask what else was available when the contract was up for renewal.
There are loads of reports of positive experiences if you put o2 broadband into the search box. Fast speeds, reliability, knowledgeable, helpful, UK based customer service people to name but a few.
Not sure about the router - I think if you use a different one, you won't have access to things which they provide, but give them a call on 0800 230 0202.