Having first hand experience on getting a software developer job in the UK as a junior/graduate, I have to tell you that almost all IT jobs here are advertised through recruitment agencies.
You don't need to send your CV to each agency though, just publish it on Monster. Putting it on Monster in a Word Document format and not forgetting to make your telephone number public are really important, since most recruitment agents are not willing to read anything else than Word documents and do not prefer sending e-mails.
Put some effort into your CV. Make it really good. Do not forget that human resources people have a totally different way of thinking than you. In my experience a cover letter is not really important in this field.
If you do these things and are indeed competent, you will have a job in the matter of weeks.