Over the past through years I have gone back & forth with survey sites. While they can be a good source of extra income, I was just too lazy to pursue them after many times being kicked off a survey for not meeting their requirements.
I have since seen the need for them and tested out the best ones to use. Each month I can make a few £100, by just sitting at my laptop while watching TV.
I would suggest signing up for as many as you can. Some pay out less than £1 per survey while others pay £3+ per survey. Sometimes it in cash while other times in vouchers.
Prolific are one of the best survey sights to join, with great payout. It is very easy to get to the £20 payout within a week or two. I suggest getting payment through Circle and not paypal as there are no fees to pay.
Opinion Outpost pays out after every 50 points (£2.50) to Paypal or Amazon and 200+ points for web vouchers.
Yougov uses credits. Payout is 4900 credits (£50) and paid out as cash.
You earn points by taking surveys with GlobalTestMarket. These points can be used towards cash (paypal), gift cards and e-gift cards. 575 points is needs for a £5 payout.
Clixsense have surveys, tasks and offers. Payout if from $10 through a variety of methods of giftcards, none being paypal or circle. People in the UK would need to use Skrill with an online wallet or a pre-paid card. Though there is a fee of 1%