Engine flooding/loss of compression

Hello,

The car was towed to the local garage, who replaced the (incorrect?) plugs, changed the oil and managed to start it. It ran fine after that, until this week. When starting from cold on a very damp morning it only just caught. Although it drove afterwards, the next day it would not start and there seems to be no compression again. In July I replaced the battery, and the garage have replaced the plugs, so I am at a bit of a loss. My plan is to fully charge the battery, remove and check the plugs (replacing if necessary), pour a little oil into each chamber before replacing the plugs, and trying again. How much oil should be used? Can anyone give me anymore help please? While I am not particularly mechanically minded, it would seem important to find out how to solve this problem, in order to avoid further towing and garage charges.

Any help will be apprecited.

I didn't find the right solution from the Internet.

References:
https://jec.org.uk/forums/viewtopic.php?t=5545
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Thank you.