As another forum member did, the first thing I did was look at Borthwicks grade cricket stats on the weetbix cricket website. His bowling on the whole has been far from impressive, with the bat in his first innings he got a ton but has barely done a thing since!
If I recall, they tried to get Tredwell on a plane ASAP, but with it being so close to Christmas I assume he/his family red lighted it. Borthwick was already in the country so was available immediately to join up with the squad and settle in. I think this had a big influence on his selection as Tredwell had little time to acclimatise and practice etc. (could be wrong on this one but I'm sure he didn't travel immediately)
I don't think rashid or Borthwick are good enough to play for England as spinners, and my opinion on bits and pieces cricketers is they have no place in a test squad. If England are going to genuinely go down the route of a 'bob-a-job' then it may as well be Samit, at least he has the advantage of experience.
We have two adequate part time spinners already in KP and Root, the choices of Borthwick, Rashid, Moeen Ali or anyone else who can send a few lobs down (I'll put my hat in the ring in terms of being able to guarantee 2 full tosses an over) can only be made as batsmen. If we throw them the ball when frontline bowlers need a rest or if we need to try something on a dead pitch and they make something happen then great, but we can't be picking these guys as bowlers.
Tredwell appears to be the only realistic option in terms of a proper spinner who is anywhere near the level we need. His problem being he isn't the match winner/breakthrough bowler that Swann was. He'll hold an end up and he won't let anyone down, he's the heir to Gilos crown. Unfortunately, we don't have the class of attack we had in the 2005 era that helped to cover for some of Giles' shortcomings. We can go back and forth about their merits as individuals (as it appears a few of you have done) but Flintoff/Hoggard/Harmison/Jones is about as perfectly balanced a bowling attack as you can get, save for a bit of left arm variety.