We couldn't. We don't sell off-the-shelf, we are selling on contract and that contract states that we will support their default build. We could argue the point at the next contract negotiations but if we simply refuse they will simply take their business elsewhere. Our concerns have been raised a number of times and will be raised again and minuted each time, so if there is a problem that comes down to their use of an outdated browser we won't (ligitimately) get it in the neck.

We are charging extra for any custom work to allow for testing and bug resolution specific to ancient combinations, and refusing to address superficial issues at all without a full change request and appropriate payment, but we simply can't refuse to aupport XP+IE8 without telling them to take their £20,000/month elsewhere.

We do have big new potential customers on the horizon, and they are more up-to-date in that respect. Maybe if these people don't upgrade soon and we do get huge new contracts, we'll be in a position to say "your choice, upgrade or go be a problem to our competitors" come the next contract round. I hope so.