doesn't seem to have clicked that when we had EU membership we could return those refugees to the country they entered the EU
I've found some stats - I might be missing something but the Dublin III Regulation doesn't look very effective to me;
Commons Library 2019 -
According to Home Office figures, between 2015 and 2018, 7,365 incoming requests were made to transfer people into the UK under the Dublin regulation, from which 2,365 people were transferred to the UK (some requests may still be pending).
This means that the UK accepted around 33% of requests. During the same period, the UK made 18,953 outgoing requests to transfer people to other Member States, from which 1,395 people were transferred abroad. This amounts to around 7% of outgoing requests by the UK resulting in a transfer.
In 2018, the UK received a total of 37,453 asylum applications, and made 5,510 outgoing transfer requests under Dublin III. Of these 5,510 requests, 209 migrants were transferred out of the UK under Dublin III, whilst 1,215 came in, making the UK a net recipient in 2018.
commonslibrary.parliament.uk/what-is-the-dublin-iii-regulation-will-it-be-affected-by-brexit/