My experience tells me that if you are here asking us this question, then even if you get the names of different agents, you will still have a difficult time getting one to sign you.
I don’t mean to be harsh, but rather to give you an important message that you won’t forget and that will hopefully help you.
You see, it’s all about your approach and even that is no guarantee that you will be successful.
How long have you been looking for an agent?
Why haven’t you found one so far?
Aside from the productions you have been in, have you been training as an actor?
Do you know what agents look for in an actor?
Do you have all your materials together and are you prepared for an agent interview?
What’s your type?
What roles do you think you would be best suited for?
What kind of acting career would you like to have?
What kind of people do you hang around? My guess is that they are not all the right kind of people who are already doing what you want to do or you wouldn’t be asking this question.
On my site for new and aspiring actors, I have an actor quiz. One of the questions is, “How long have you been acting?” Another question is, “Do you have an agent?” More often than you might think, there are people who fill out the entire quiz and who have been into acting for more than 5 years and who still don’t have an agent. The question I have is, “Why not?” After a few weeks or a few months, the answer, “I don’t know how to get one.” is acceptable, but not after five years! Not after 6 months even!
If a person doesn’t have the approach that if they don’t know something they have to figure it out, then they will never be much of a success, not only in acting, but in anything else they choose to do in life.
Change your approach. Change your way of thinking and I’m willing to bet that you will start to see positive results in your acting career as well.
Have a look at this page on my site. It talks about different aspects of an acting career including how to get an agent. http://www.actingcareerstartup.com/teen_acting.html
Even if you are not a teen, read some of the titles you find interesting anyway.
One last thing. You said you need an agent anywhere in the UK. Are you sure? What if you live in Manchester and your agent is in London and most of the auditions they call you for are in London? Are you really going to want to be trekking down there frequently for auditions? That will cost you time and money. Do you really want to do that?