[evie2]

Is there anything I can do with them?

[arugula]

You can still stew them.  Just how unripe?...... 

[evie2]

Thanks for putting me in the right place   Hard and green I'm afraid   I'm so upset because both trees were weighed down with fruit when we went on holiday and when we came back all the ripe ones were gone, not one left on the tree or on the ground

[arugula]

I'd say cook them like that with plenty sugar, make wine or make a chutney. My Mum used to make a fine plum chutney with plenty chilli in it too. 

[evie2]

I'll look for some recipes

[Dilly Dom]

Plums need to be quiet firm for jam.

[evie2]

These are very firm 

[sunshineband]

If they are still on the tree you could wait for them to ripen a bit 

[evie2]

I'm not sure they will now

[sunshineband]

I'd give them another couple of weeks as thye might increase a bit in size too