They really expected to have to fight and expected to die just to delay the Germans. Many (like my grandfather) were WW1 veterans and quite liked the P17. By 1942 they could have probably defeated a Sea Lion by themselves and by 1944 have made an Overlord hard work.
To be fair, given what the Germans would be bringing ashore, namely disorganized scattered light infantry, and who a lot of the Home Guard was, namely WWI vets with two pertinent skill sets, namely digging in deep and shooting Germans, I suspect the Home Guard could have seen off any plausible Sealion by themselves.