Finding competent, reliable, affordable and user-friendly tradespeople is an issue most people have to deal with at some time. There is no foolproof answer: there are professional bodies such as Gas Safe Register, NIC-EIC, NAPIT etc, commercial certification schemes such as Checkatrade, Trustmark and some local authority (but not Reading) approved trader schemes, directories such as the Little Green Book and informal, user-contributed directories such as the University's Handy Persons web page; and there is word-of-mouth recommendation, either person to person or asking on mailing lists or social media.
The Little Green Book has listings of tradespeople recommended by customers (although the tradespeople also have to pay to be listed in the directory. It is organised into sections for Reading, Wokingham and other nearby areas.
The University's Handy Persons page used to be a useful resource but it is no longer maintained (and not available from the University's own site now unless you have a Uni login - this link is to the Wayback Machine's saved copy).