I can't buy buttermilk in Spain and it appears very frequently in your recipes. Would yogurt and skimmed milk be a substitute?
You could try making your own by adding 1 tablespoon lemon juice to 8 fl oz skimmed milk. Leave to sour for 10 minutes before using. Alternatively you could try the following:
Please bear in mind that we have not tested any of these substitutions in Delia's recipes though.