Two important notes:
1. Boris Johnson, PM May's heir apparent, was Foreign Secretary from July, 2016 to July, 2018 - during much of the time that GCHQ (Britain's NSA) eavesdropped on candidates Trump and Cruz and President-elect Trump. GCHQ reports directly to the Foreign Minister.
2. GCHQ's spying on the American political candidates likely began in 2015, under then-Foreign Minister Philip Hammond. We believe this because GCHQ Director Robert Hannigan traveled to Washington, DC in 2015 to meet with CIA Director Brennan - an odd thing since Hannigan's actual US counterpart (in signals intelligences) was NSA Director Rogers, a non-coup plotter. This curious fact supports the belief that CIA enlisted GCHQ to conduct the actual eavesdropping on the CIA's political targets within the United States.
So... Was Boris Johnson complicit in GCHQ's role in the failed coup against President Trump? Or is Boris Johnson a Trump ally who discovered what his predecessor began before Johnson took over as Foreign Secretary? Time will tell.
Thank you for that additional.