[user104658]

Originally Posted by Barker

Do you not realize that's just one bookmaker? There's many and every other one has Callum at far safer odds than the twins.. But then again you'll do anything to put down Callum so fair enough

Betfair isn't a traditional bookmaker, it's more like a betting exchange... So the betfair odds more accurately represent public opinion which is a good indicator of what might happen in a public vote outcome (unlike, say, a horse race where public opinion means less).

Highstreet bookies use a combination of money placed and trader knowledge / experience to set odds. So whilst a shift in betting will alter odds, the traders will also try to pre-empt betting patterns before they occur and alter odds accordingly, by following developments as they happen.