The Royal Academy of Music and the Royal College of Music hold many free concerts, mostly at lunchtime or early evening and there are also free concerts at lunchtimes in churches, such as St Martin in the Fields. Check the length as many concerts are short, so not worth travelling to unless you’ve are shopping or work nearby. I’ve mentioned the drama schools’ free plays (see the new LAMDA season) but commercial theatres also give away seats via audience filling or ‘papering’ schemes. Most productions are in fringe theatres but larger productions do come up, mostly at very short notice, for previews and press nights. These schemes often cost money to join and there’s a booking fee of around £3 for a seat. I am a member of two of these: one was advertised on my work intranet and is free to join; the other has an annual fee. As part of their conditions, I will not name either, not will I ever mention that I have been to a play or concert in this way. If you work in the NHS or other public services you might well find such a scheme available to you. Otherwise, these schemes are open to all (in alphabetic order): Audience Club, Play by Play, Showsavers Plus and Theatre Club. All limit the number of members and I am not sure which are open right now.