It's supposed to be regularly every 8 years to keep the population in each constituency roughly the same, but the Constituency boundaries last changed at the 2010 general election. Regular reviews of parliamentary constituencies have been held since the House of Commons (Redistribution of Seats) Act 1944. Previous boundary reviews were held in 2013 and 2018, following the passage of the Parliamentary Voting System and Constituencies Act (2011). If implemented, these reviews would have reduced the number of seats in parliament from 650 to 600. However, neither was implemented. The 2013 reforms were blocked by MPs and the 2018 boundary review was scrapped in 2020 after the government argued that Brexit would increase MPs’ workloads.

So, the answer is they should be reviewed regularly (next one in 2031) but their reviews can get smashed by down by Government.

Gerrymandering is less of an issue here because constituencies need to have 69,000 - 77,000 people inside them and these are usually based around a small geographical area. I'm sure it does happen a little bit, but not as often as it does in the States. :o)