If you are in London this October try to get to the RHS show on 21 or 22 October as 12 botanical artists will be exhibiting a very wide range of subjects (.pdf scroll down).
Just to make people aware well ahead of it happening, the RHS Botanical Art show in London will be on 27-28 February in 2015. It will be a stand alone show and not part of the Orchid Show in April as it was this year.
Also worth a look if you are in London is the new exhibition at Kew Gardens - I've not seen it yet but there's an interesting photo montage of Fritillaries to compare with Rachel Pedder's epic 18 foot long work.
If you are interested in scientific botanical illustration then there is an interesting one day meeting at the Linnean Society on Thursday 29th January 2015 called 'Systematics & Botanical Illustrations'.
If you are looking for a painting course on botanical art then Fiona Kane has made a directory of those available in the UK here. The links tab has further information, including web-based courses.
I've added a page on all the botanical art exhibitions I can find mentioned on the internet in the UK (see sidebar: 2014 Art Calendar) - if you are aware of any more then do let me know and I'll put the details up.
I'm now on Facebook here posting about botanical art and on Twitter as @botanicalmartin chatting about plants.
Do say hello.....