Never seen John Bishop but I enjoy his TV stuff.
I have eaten at the Karma Sutra on Sauchiehall St many times and it is possibly its own worst enemy, because they often have a guy outside dressed in Bollywood gear handing out fliers and trying to get people in. And if you're unlucky there will be a stag / hen party in full swing, but you can't blame the restaurant for that.
The food is as you say quite good, but unless you go for the pre-theatre, you need to be hungry: I once ordered a chicken chaat starter followed by chicken jalfrezi, brinjal bhaji, pilau rice and a naan. The chicken chaat would have been a great "sharing dish." For a rugby team. To finish me off, the naan was the size of a dustbin lid. I had to ask for them to bag it all up, but it did two lunches in the office later that week, so nothing was wasted.
If you're looking for a decent curry in Glasgow, you might want to try one of the following. They are all a bit different and they cater to different tastes, but I have put them in order of preference:
The Wee Curry Shop
Heera (Charing Cross)
Charcoal
Bombay Blues