The Remain campaign (not the same thing as the government) is looking for the support of respected voices, what's the problem with that?
It's fair game. The Remain campaign is free to contact religious leaders and ask for their support, and they're free to say either yes or no.
(If you think they're not free to no, then I'd suggest British democracy has bigger problems than the EU, which for all its fault does uphold free speech...)
I get Leave are upset that they can't get anywhere near the amount of respected voices on their side. But the reason is not the existence of some government conspiracy to secretly coerce everyone, the reason is that religious leaders (and academics, etc) are overwhelmingly in favour of Remain, not Leave.
The Church of Scotland already has taken an official position in favour of Remain, so this is not exactly a surprise.
And so what if Church leaders feel so strongly about this that they want to publicly come out in favour of Remain? Of course the campaign is encouraging them and coordinating behind the scenes. It's fair game.
Do you really think so little of British democracy that you believe the government can coerce academics and church leaders into taking positions against their will? If academics and religious leaders want to say something, then they will. If they don't, then they won't. Freedom of speech still exists in this country.