I think that what OP is asking and the local visa agent wherever, has suggested, is that the OP not disclose the Schengen denial to the UK. Thus, calling the British Consulate is disclosing what the visa agent is suggesting not be disclosed.

Nonetheless, don't get your advice here. The real question is whether the UK, despite being non-Schengen, has access to and checks records of Schengen visa denials and would thus see OP's action as fraud and then definitely deny the OP.