12 First Class and 4 Large First Class stamps every month (worth £8.52) for taking part in this - not a lot of work involved if you live fairly near a post box:

How Quick is Royal Mail?

10,000 people at addresses all over the UK participate in the official independent measurement of Royal Mail's service

TNS Research International is commissioned by Royal Mail to deliver this project
.
We're always looking for more people to take part by representing their own postcode area.

Interested?
To find out if you're eligible and receive more information about the project (including the incentives that we offer) please complete this short questionnaire.

Please click here to view Royal Mail's confirmation of the authenticity of this project:
https://rmselfrecruit.research-int.com/
Questionnaire/Documents/Royal%20Mail
%20Introductory%20letter%20headed.htm

FAQ - http://rmpanelzone.research-int.com/
FAQ.htm

To take part go to:
https://rmselfrecruit.research-int.com/Questionnaire/qstIntroductionPrivate.aspx

Hope this helps you guys out :-)

P.S you have to be 18+