I am kicking myself. I am going to London Monday, so looked on the National Railway website to book my ticket and it took me directly to the London Midland booking page. The cheapest tickets highlighted were two singles totalling £26 so booked them. Then afterwards I thought might as well book the ones for the following week too. So didn't bother with National Railways, went straight to the London Midland, which this time took me to the home page as I wasn't being redirected and it turns out if I print out a voucher I could have got return tickets for £15. So that's £11 down the pan, I hate that sort of wastage. Still at least I bought my second ones through the offer been worse if I had missed it completely.
So if anyone is booking tickets to travel during the next couple of weeks, make sure you check the home pages of rail providers, don't just use a generic booking service