Viewing the football isnt strictly legal, as UEFA and the FA sell the rights to one or a collaboration of broadcasters, on the basis they are only to be sold, and viewed in that particular country (I understand all this only too well, the crap we had at TopUp TV, and the demands we had placed upon us by BSKYB to increase our encryption security when we launched Sky Sports, meant use developing and releasing countless software updates to fulfil compliance agreements - and practically it all boiled down to the terms of the football and Twenty20 rights agreements!!).
As BSKYB/ESPN and the BBC own the rights for the FA Premier League television transmissions in the UK, technically, viewing it on another service provider (even Setanta as they only maintain the rights for transmission in the RoI now), is illegal.
You have to ask yourself though, who is going to know; and even if somebody informed the relevant authorities, a. would they be bothered doing anything - the FA may force encryption on FTA channels/cease the contract with PPV channels - but its unlikely they would even bother doing anything more than sending you a letter informing you how it is against the law, and how it adversely affects these poor underpaid footballers and the clubs etc, and b. they need to prove it in any case lol.
So essentially, nothing to worry about in using the service, but perhaps a moral issue more than a legal worry?