First of the month:

• Thursday

White Chape http://www.firstthursdays.co.uk/ Last of the month:

• Wednesday
  • Science Museum http://www.sciencemuseum.org.uk/visitmuseum/plan_your_visit/lates.aspx
• Friday
  • V&A http://www.vam.ac.uk/content/articles/f/friday-late/

etc

• Dino Snores for adults http://www.nhm.ac.uk/visit-us/whats-on/after-hours//dino-snores-grown-ups/