BBC Radio 4 are inviting submissions from writers "new to radio" for their annual season of short plays, Opening Lines. By short, they point out, they mean around a maximum of 2000 words, with an emphasis on narrative rather than dialogue. They are also at pains to point out that they will be looking for plays that successfully link the end back to the beginning. Helpfully, the website - see here, folks - gives examples from last year's entries.
The submission window closes on December 14th 2012. For full details, see the link above.