If, and it is a big if, Saints can repeat last years performance then they are our only real hope. Sarries might but I suspect that they could have their buttocks presented to them by the Irish/French teams who would be able to counter Sarries attacking play and out do them in the forwards stakes as well.
The other "top" English teams simply can't do it: Tigers are on a downward trend that is going to be hard to reverse in time for the pool stages, Glaws aren't good enough on away form ATM so as soon as they lose a home game they're toast, Quins aren't bad but aren't Heine standard and Bath have a front row so poor ATM that Cian Healy with rip them to shreds and we'll just give up and return with our tails between our legs cursing the fact that we've blown a large amount of money of a FH and not bought a decent Front row.
Finally to do the double you have to win the Prem. Out of the sides I would see as likely/nailed on top four finish: Bath just won't, Quins probably won't, Saints have had too poor a start and they will lose another wave of players to the 6Nats, Tigers could... just, Irish won't, Glaws won't. Sarries will.
So basically... if ever there was hope of an english club dong the double it isn't this year.