The previous Labour government (1997-2010) introduced the Regulation of Investigatory Powers Act 2000 (https://en.m.wikipedia.org/wiki/Regulation_of_Investigatory_...), which amongst other provisions includes key disclosure rules (https://en.m.wikipedia.org/wiki/Key_disclosure_law#United_Ki...). The burden of proof in key disclosure is inverted (the accused must prove non-possession of the key or inability to decrypt), which was somewhat controversial amongst people who cared at the time (activation, i.e. actual use if RIPA III provisions, began in 2007).
The same Labour Government ran the Interception Modernisation Programme (https://en.m.wikipedia.org/wiki/Interception_Modernisation_P...) (you may recognise this or "mastering the internet" from the Snowden leaks, although IMP was not a secret) and proposed legislation to enact part of it: https://en.m.wikipedia.org/wiki/Communications_Data_Bill_200.... This never made it into law.
I think Labour are on board with this, and the senior civil service (those at the top levels who work with ministers or close to those who do) don't change in the same way US administrations do. It might be the case that this bill runs out of time in the current parliament and is not picked up by the next government (this can happen even if the same political party holds office) but the idea will be back in some form one way or another and I suspect will make it into law.