In July 2018, HMRC updated its guidance on trust record keeping. This is a mix of tax and anti-money laundering requirements.
Dormant trusts may not have to complete a tax return or trusts register but there are still record keeping obligations, such as under para 44 and 45 of the The Money Laundering, Terrorist Financing and Transfer of Funds (Information on the Payer) Regulations 2017.
I recommend that all trusts have an annual trust meeting, asset review and simple accounts (even if just one page). Whenever I am asked to advise on a historic trust problems (eg missed IHT charge) a common theme is lack of annual meetings and accounts.
Here is the HMRC website link https://www.gov.uk/guidance/trust-record-keeping-for-tax-purposes
And a PDF version safari-30-jul-2018-at-1021.pdf