Sammy - is there some way that you could delicately ask whether it's the money? GPs are only contracted on the NHS to do reports when asked for them, but they might be willing to do one if you pay for it.
If you go to appeal, it won't matter whether the DWP are interested in reports from others, it will be up to the tribunal judge what evidence the tribunal takes into account, so if the DWP doesn't give you the rate of DLA you're hoping for this time around, there's a second bite of the cherry if you appeal.
