This is a topic close to my heart as my husband is a ‘real’ bag collector for two ‘real’ big named Uk charities. These are two of the most well known charities that have shops in nearly every town in the UK.
He has been a registered collector for many years, who does this as a job, and he picks up and delivers bags which go directly to the charity shop concerned where the items are sold in the shop.

Obviously this huge scam being carried out is causing alot of problems to existing charity shops such as these as the donations are down drasticaly. Collectors such as my husband of course are finding it hard too as their wages are calculated on the number of bags they collect.

If you wish to donate, and also wipe these scammers out, then the best thing to do is (a) as others have said, take your donations directly to your local well known charity shop.
Or (b) just put your donated clothes in an authentic registered charity bag which you know has a shop in your area, to be collected by an autentic collector.

From our experience, unless the donations are going straight to a shop, then these bags are most likely to be some sort of money making scam.

High Street Charity shops are finding it very tough at the moment, so please support them and not your local second hand clothing businessman.