People in a party of left-wing English radicals initially switching sides (9)

'people' is the definition.
The answer is an example.

'party of left-wing english radicals initially switching sides' is the wordplay.
I cannot quite understand how this works, but
'party' could be 'revel' (I've seen this before) and 'revel' is found within the answer.
'left' could be 'l' (common abbreviation) and 'l' is found within the answer.
'wing' could be 'r' (r is abbreviation for right) and 'r' is found within the answer.
'english' could be 'e' (abbreviation) and 'e' is found in the answer.
A single letter 's' remains which might be clued in a way I don't see.
This explanation may well be incorrect...

'in a' acts as a link.

Can you help me to learn more?