Having only recently ensured that British police could exercise their powers on ships in British waters, the UK has been quick to ensure that any criminal acts committed on a spacecraft launched from the UK would, if an offence in the UK, will also be an offence if carried out on the spacecraft. So that’s alright then… See section 51 of the Act.
http://www.legislation.gov.uk/ukpga/2018/5/section/51/enacted