The Small Charities Coalition have lots of really useful guides, toolkits and resources covering topics such as Monitoring and Evaluation, Accounts & Finance, Campaigning, legal and fundraising

Joining the Small Charities Coalition entitles you to a range of benefits. Membership is free and open to any UK-based charity with an annual income of under £1 million.

https://www.smallcharities.org.uk/resources-evaluation-impact/