Do they charge high fees to join or something so they lock the traders in
or is it because the exchange is based in England ?
if price differnces lasting longer than couple of minutes, then something is wrong with the exchange. In this case it is high withdrawal fee and especially long withdrawal time. If you look at their official bitcointalk thread, you will see alot of complaints that withdrawal took days, weeks or even months (or not even possible if you are based in US)
They have a special buy/sell section in their website. The trick is that you can only buy BTC for 100 / 200 / 500 / 1000 USD there so it makes harder to calculate the real rate of the BTC. Usualy they sell for about 10% over the market rate. The next interesting thing is that they are also selling BTC for the rates over their own exchange! For example right now the BTC price on coinmarketcap is 11.9K, the price in Bitfinex is 11.7k (cmc price is not accurate so I just also mention bitfinex), cex.io price is 12.5k BUT if you want to buy BTC thru their "Buy/sell" section you will get the price about 13.5k that will be shown as 0.0074 BTC for 100$.
I'm sure that the exchange is not located in UK. Remember that the United Kingdom is a popular offshore zone. Their CEO is from Ukraine. Here is his linkedin: inkedin.com/in/olutskevych
Anyway I do not recommend using CEX.io. This exchange is shady and dishonest.
