Cherry tree question/problem

We have a cherry tree in our garden, inherited when we moved in 3 years ago.  It's about 30' tall; we don't know the variety but it bears a small amount of small dark fruits which we've never eaten as they always seem to be high up and the birds get there first

In previous years its looked a perfectly healthy tree in full leaf through summer and lots of spring blossom .  This year, however, up until now its still completely bare of leaves and no blossom.  It's covered in tight, healthy (looking at them, having broken a few off) blossom buds - in short, it looks as I think it should look much earlier in the year.

I've never really noticed exactly when it does blossom/come into leaf in previous years... it's just "there" and has always been healthy.  We're in the south east where it's been exceptionally sunny/warm.  Are there some cherries which come into leaf/blossom later than others and I've simply not noticed this in previous years?  Or is there more likely something wrong with it?  It looks very conspicuous, being the only tree in the vicinity to be completely leafless!

Many thanks.