Thanks for the link.
From what I understand, for medical devices which have a CE mark, nothing much will change until 2023 (assuming that the manufacturers of those devices can obtain a CE mark - currently through the MDD, soon under the MDR).
Custom and in-house manufactured devices will need to meet the requirements of the UK 2002 Medical Device Regulations. I expect that these will be aligned with the EU MDR etc in due course once the new UK Medicines and Medial Devices Bill has been passed. There may however, at some point, be some divergence between the EU and UK medical device regulations. If/when this happens, manufacturers would have to comply with two different regimes to get access to both markets.
As stated in the guidance, there will be an additional requirement for medical devices to be registered with the MHRA following a certain grace period.