I think wind damage and lack of water are more likely to have caused the leaves to wither and fall off than frost as Acers are quite frost tolerant. A lot of peoples (mine included) Acers have had withering leaves caused by the dry weather.

That wouldn't explain why the rose branch died - unless the branch had been damaged near the base, something you might check for. I'd certainly be asking the neighbour precisely which weedkiller he's used, and how it was applied, via sprayer or watering can.

Thanks for the answers, the acer is now looking even worse than on the photo and for all intents and purposes I would say is not far off dead. It certainly isn't because of lack of water and the climbing rose next to it on a fence got progressively worse over a couple of weeks, but is showing signs of new foliage. If it was wind damage, is there any chance that it will recover and get new leaves, or should I write it off as finished?

If that's wind damage I'm a monkey's uncle, frankly - something's happened to it, and isn't frost. I suspect it will continue to die back, but I'd leave it a little while just to see what happens.

The acer now looks like nothing more than bare dead branches and low and behold the climbing rose I had isn't doing very well either along with a separate rose bush, which in the past couple of weeks seems to have gone down the same road!!! Is there anywhere I could have them "analysed" just to see what exactly has happened to them. We are in a bit of a dispute with our neighbours at present and I can't help but think that out of spite they have sprayed my plants with something, but obviously I have no way of proving anything.

Something's just occurred to me, and it should have done earlier, sorry - verticulium wilts. This is a disease that Acers are prone to, its a fungal infection, but it can spread to other plants. Dig out the Acer, as its dead anyway, and strip back the bark as much as possible - you're looking for brownish black staining, sometimes purplish streaking of the wood beneath the bark. Roses don't usually suffer with this though, but its not impossible if that's the problem with the Acer, so also remove the dying stems of the roses concerned and do the same. If you find it, that's what it is, and if it is, its a serious problem. You'd need to remove all affected plants (provided you're sure that's the issue) plus the area of soil their roots inhabited. Then there's a list of plants you shouldn't replant in the area because they're susceptible, of which Acer is one. Also clean and sterilise all cutting tools (secateurs, loppers, etc.) because it can be carried on those too.
This assumes that no nasty treatments have been applied to either the plants or the soil in the area by anyone. As for testing plant tissue, I believe the RHS offers this service to members of their society, but contacting them would be a good idea even if you're not members - they may be able to tell you where else you can go.
The other possibility is honey fungus - did you notice any honey coloured toadstools in the area last September/October? Do you have any dead tree stumps or similar nearby?