It's not UK based and it is more specifically on evangelism rather than missiology in general but Bryan Stone's Evangelism After Christendom is a must.

Another one not aimed at the UK but more like another Bosch is Bevans and Schroeder's Constants in Context.

One that is on the UK is Duncan McLaren's Mission Implausible which looks at missional responses to seculrisation drawing on the insights of sociology of knowledge.

If you let me know what aspect of missiology you are interested in (social action, emerging church / fresh expressions type stuff, mission and the bible) I'd be more than happy to make a few suggestions

emerging church wise - can i suggest mission-shaped questions or evaluating fresh expressions or remembering our future: explorations in deep church. The best text on emerging church is Emerging Churches by Gibbs/Bolger

A lot of writers around the subject seem to be re-discovering Lesslie Newbigin, but rather than wonder which of his many books to start on try Paul Weston (Ed) "Lesslie Newbigin: Missionary Theologian, A Reader"

I would also recommend Stuart Murray, "Changing Mission: Learning from the Newer Churches" - UK context, anabaptist learning from emerging church

and Ann Morisy "Journeying Out" (Bit too Anglican but there are ideas and thoughts than can be translated into your context - I was particularly struck by cascades of grace.)

I'm with Craig for "Changing Mission" by Stuart. It's concise and is typically well referenced, so offers loads of starting points and suggestions for the things that interest you.

Also "Church Planting" by Stuart is the most in depth look at the uk scene, and is very thorough and is a theoretical approach to his subject (His practical handbook on Church Planting is out soon, published by Paternoster).

I've read quite a few on mission and evangelism which I've listed on my blog: here: http://graham.doel.org/index.php/2008/05/02/aprils-books/ and elsewhere as well.