Most of the sources I can find suggest using Cheddar if you can't find anything else. I've been trying to find an answer to this question myself, because I want to make Glamorgan sausages.
The distinctive characteristics of Caerphilly cheese (which I admit I've never had the chance to try) seem to be that (1) it's on the dry side and has a crumbly texture, and (2) it's slightly tangy. Monterey Jack cheese is tangy, but not crumbly. Mexican farmer's cheese is crumbly, but not (at least IMHO) especially tangy. I plan to try a mixture of sharp white Cheddar and finely chopped Monterey Jack, and hope it turns out all right. Hope this helps!
Lancashire Cheese
You should use Swiss, Provolonge, American Cheese, Fetta .. there are many types of cheeses you could use This depends on how you intend to use cheddar in your recipe If its for a cheese sauce, I would probably use something like a gouda, which is used in the making of Swiss cheese fondue (which is essentially a type of cheese sauce). It does have a slightly more nuttier flavour, but is a milder cheese. If used as a topping which is to be melted like on a pizza, then mozzerella would be a good substitue. If for making a good old fashioned cheese on toast. I would actually combine mozzerella with some parmesean (mix them together in blender with a bit of cream to hold mixture). The mozzerella would give a nice stringy soft texture and the parmesean would add flavour to the mild taste of mozzerella.
No. Plain yogurt is a good substitute for sour cream. A substitute for ricotta cheese is cottage cheese that has been drained of excess water (use cheese cloth or seive).
A good substitute is Caerphilly Cheese from Wales which is a pale crumbly cheese made from cow's milk. It has a similar texture and taste to Lancashire Cheese.
Jarlsberg cheese, Leerdammer, and Maasdam cheese are all good substitutes for Emmenthaler.
Sour cream
Shredding:Cottage Cheese Melting:Pizza cheese
I have personally found that Colby works well as a substitute.
many people use fontina but it does have a milder taste
Lemon juice
I would think not because whip cream is sweet. Sour cream has a more tangy bitter taste to it.
goat cheeze or a mild bree` would be good.