When you buy goods you enter into a contract with the seller of those goods. Under the Sale of Goods Act 1979 goods must be:
1) 'as described',
2) 'of satisfactory quality', and
3) 'fit for purpose' – this means both their everyday purpose, and also any specific purpose that you agreed with the seller
Based upon the above principles, if you specifically asked would it accept digital signals and were told yes....and this fact was also advertised on the goods, then you can reasonably expect the set to be fully capable of<u> independently</u> accepting digial transmission, as told & was advertised on the goods at the time of sale. ( principle 3).
The fact that digital signals were not being transmitted at the time of the sale gave you no reasonable opportunity of testing the TV's capability, therefore as these circumstances were fully outside of your control you had to take their word for this fact. I believe you have a claim that the TV is :
1) Not fit for it's intended purchase. (although you could not reasonably test this fact, until present day).- (principle 3)
2) Not as described, in that the set is incapable of accepting digital signals, therefore they either accept it is faulty, otherwise they leave themselves open to an accusation of misleasding advertising. - Not as described (principle 1)
That said, you can expect heavy resistance from the retailer but if you wished to stick to your guns I believe you would have a successful claim, should this need to go to court.
Rights under the SOG can last for up to Six years, taking account of the duration of time lapsed since the purchase in 2006, it has not been until recently when digital signals started, that you have in fact been able to test the set, therefore you were taking their word up until now that the set was capable of performing the functions for which it was purchased....this is indeed the first opportunity you have found to test the set and discovered their word is not in fact the truth...on these grounds in my view you do have a valid claim.!
If on the other hand, you could have reasonably tested this TV set back in 2006 and had failed to do so up until now, that would be a completely different matter and your fault, in which you could fully expect your claim to be invalid as under the SOG act you did not make the retailer aware soon enough.