If the soil around it is not dry or you haven't had a recent frost then I would suggest that as it can be slightly deciduous then it might naturally be about to lose its leaves. There does appear to be new shoots in your photo so I wouldn't worry for the moment.

Thank you, Jimmy. With all the rain it shouldn't be too dry though there is the, still living, cut down ash stump the other side of the fence. So there are a lot of roots in that area. I managed to persuade the neighbour last year to cut down the tree which was massive but he isn't bothered about killing the trunk. It will grow again and VERY quickly.
For now I'm enjoying the space.

Oh dear Arbuthnot, that's sad news - the blessed thing will send up multiple shoots now - good luck with persuading him to chop them off as and when"!

Just from looking at pic 1. I would say it's planted too deeply. I say this because I cannot see the root flair. The top of the rootball must be at ground level, but here it seems to be way down yonder. It's planting hole seems to have collapsed may be due to excessive rain, causing it to sink. Gently lift it out of the ground and give it a new planting hole with the rootball just below the surface. This is critical. You can plant it a little high to make allowances for it settling. Planting too deeply is a death sentence. Full/partial sun for optimal flowering & more space between the fence. Keep it well watered.

Thanks, Bathgate. My husband did go round putting compost/manure on the beds so that would be why you can't see the rootball. When it stops raining I shall follow your suggestion. Thanks again.

Great! It's should bounce back quickly. It's not too late. The roots need to breathe. Tell him not to put compost/manure right up against the main stem. This can cause decay. Give the poor tree a clearing of a few inches around the main stem. Viburnums are tough vigorous stalwarts. It may even reward you with blooms this year.