If you mean "does it appear in dictionaries and has it a sound pedigree as a word", then the answer is yes. I found it in the Oxford English Dictionary - with one example given from 1660.
If you mean "if you saw this word in context would you know what it meant", then again the answer would be yes. It means capable of being delegated, as you would expect.
If you mean "is this word regularly used by ordinary people?", then I suspect the answer may be no.
But it is a genuine word, it appears in dictionaries and it is regularly used in specialist contexts.
And yes, delegable is used in British English (BE). Here is an example:
The Law Commission concluded that in relation to trusts which were not charitable trusts the characterisation of powers of investment and some powers of management as in all respects fiduciary and therefore non-delegable was outmoded and that in general terms the proper distinction to be drawn in a modern law of trusts for the purpose of ascertaining whether a particular function ought to be delegable was between administrative powers (which would be delegable) and distributive powers (which would not).
that's what i was looking for, thank you very much
Actually, the word is quite understandable in the context i am using it (computer security: delegation of privileges, for example). And in fact, it is commonly used in technical literature (mostly american), I just wasn't sure if it was correct in british english, genuine and appering in dictionaries (as you said).
Again, thank you very much for your clear reply, and the quote