Here are some orchestras, ensembles (and summer schools!) that we know if. ViolinSchool doesn't directly endorse any of these groups (apart from our own Violin Orchestra!) so be sure to check each organisation out thoroughly first to make sure it's the right choice for you.
Dartington Summer School
East London Late Starters Orchestra
The Violin Orchestra
London Gay Symphony Orchestra
The most comprehensive list of UK orchestras can be found at http://www.amateurorchestras.org.uk/ - take a look at this wonderful website for more information!