Can I use lager malt for yorkshire bitter?

I'd say just go with what feels right.

Good advice I suppose - it's not a million miles away from the recipe so I'd imagine it will still be drinkable, if not a decent 'bitter'.

Only got Gervin ale yeast or Saf 04. Other alternatives are Saf lager yeast or Whitelabs kölsch yeast. Out of what I have, I'm thinking that either the Gervin or Saf 04.

If something else would make a notable improvement I'd be ok to order something specially.

I'd go s-04, gervin is pretty low on esters so it won't taste very British.

Cheers Rob, much appreciated. The Saf 04 seems a bit of a beast, so quite happy to use that again - it got my stout going great guns after the Nittingham didn't fire up.

S04 and Nottingham are both flavor and aroma neutral, next time experiment with a malty ale yeast.

Do you think I'll get a MUCH better result using a specific bitter yeast? - I could fairly easily order some Wyeast.

You would but I do feel you may as well just go with what you've got for now, it's never going to be bang on with the wrong base malt, so just brew the damn thing!