Well, I just had to try it. Today I popped back to the same area where I dug the silver three pence and those sixpences yesterday. I felt sure I was going to find some more silver.... not only didn't I find any silver coins, I never even found one pre-decimal coin. All I found was 52p in decimal coins. That's metal detecting for you.
Looks like I'll leave that area for a bit. I will try it again after some heavy rain and because all the finds are very shallow I will use my Ace 250 with the standard coil fitted to get down between the trash easier.