Useful CAA leaflet.
In the meantime, even those correcting incorrect posts may miss something. ANO 2009, schedule 8 allows a CPL holder to fly as pilot in command of any flight except a multi-crew public transport flight - so a multi-crew aerial work, private, positioning or test flight would be fine, as of-course is a single pilot public transport fly. There is a further restriction mind you - without an IR, a CPL holder can't fly public transport in aeroplanes above 2300kg unless the take-off and landings are no more than 25nm apart.
There are a few loopholes - for example there's no microlight CPL, so almost all microlight instructors (under a CAA exemption) are quite legally paid to fly with PPLs. CAA itself allows its own staff to fly on business so long as they hold an IMC (the latter being an internal requirement, not a legal one). Many BMAA and LAA member/PPL holders regularly conduct test flying which technically is an aerial work activity, again with CAA issued exemptions allowing this.
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