Arbitrage Opportunity on Scottish Independence Stock?

As I write this, the 'Scottish Independence Referendum = Yes' stock is trading on Ipredict for around .40 a share (which can be understood as = c. 40% chance of a yes vote). If you look at the British bookie sites, they are offering a 'Yes' bet at a probability of around 65% (15/8 on Paddy Power and 2/1 on Betfair). If someone had an account with both Ipredict and one of these bookies, they could buy it 'here' and sell it 'there' for a guaranteed 20% ROI. Or at least I think that this is the case (please explain if I am wrong).

BTW, I tried to post this under 'active stocks' but for some reason recieved a message telling me I didn't have permission to do so, so I posted it here.

Yes, you are correct.

In the last US presidential election, InTrade consistently showed about a 10c premium on the Reps. iPredict would essentially track InTrade up and down.

I guess the 10c difference was representative of the cost of transfers between the two systems.

Some interesting developments here:

Today a poll came out which showed the 'no' to independence vote ahead. That contradicted a 'surprise' result in a poll a few days ago showing 'yes' ahead (and which prompted me to look into this stock). Perhaps in response to this new poll, Ipredict shares in 'yes' to independence fell to around .25 (= c. 25% chance of a yes vote). But, interestingly enough, the British bookies have RAISED the odds of a yes vote to = c. 75% chance of a 'yes; vote (5/2 at Paddy Power and 4.1 at Betfair). Which means that that there is now an even greater arbitrage opportunity in this stock: (if someone were to buy 'here' and sell 'there' they could lock in a guaranteed ROI of around 50%).

A couple of final points:

(1) Given the share volume on Ipredict, I don't know if this trade is practical (For me, Ipredict is more about 'fun' and intellectual stimulation than money)
(2) If I had access to a bookie that would give me these odds on this referendum, I wouldn't be talking about it!
(3) Yes, I know Betfair is a betting market, not a bookie - just using that term as a shorthand.

You sure you have that the right way around?

PaddyPower has 1.28 to fail, 3.5 pass = ~ 75% of a NO vote.
Betfair is very similar.

Whoops! Well, that is totally embarrassing. I was dividing 3/1 (for 3 to 1 odds), when I I should have been doing (3/1-1). Embarrassing!

Double Whoops! Make that ((3/(3+1))-1)...

our market is broadly in line with the bookies