@Paintbox
Friend does like the band, maybe that's it, she thinks I'll take her. Still weird though as she knows I wouldn't like it. Oh well. Maybe we will have to be unavailable to go for some reason.
She thinks you will take her?
Has she got a ticket as well? 
I would go (probably) if it was a short bus ride from my house, and I wouldn't have to spend more than a tenner in total with travel and drinks/food etc.
But most concerts I have been to have been 40 miles away, cost £15 return on the train, and sometimes involved an overnight stay. Minimum £40-£50 for a room. And that's not including food and drink.
So yeah if it wasn't someone I wanted to see, I'm afraid I wouldn't go.
There is no way to 'give the tickets back' to the giver, without causing offence. That said, it is bizarre to buy concert tickets for someone unless you know they love the band or singer.
I would think about selling them and saying you went. Just say 'yeah it was great.'
Tricky one.