a big ask BrE informal
a tough ask BrE informal

This in itself is a Big Ask, as Friends of the Earth would say.

But if you live elsewhere it is, in football parlance, a Big Ask to identify all nine airports that now market themselves with London as a prefix ( I mean, are there nine airports using New York in their titles?)

Now I’m asking – and I know this is a Big Ask – our players and fans to show the same resolution, courage and stubbornness with which they’ve helped to turn around attitudes in this country, to help Ukrainians of goodwill to do the same.