It's different when politicians are saying it about the Prime Minister.
No it isn't. I'm not sure the majority of the public consider the difference. Most people do not concern themselves with nuance of politics, they go for headline and soundbite.
The 'PM is a bigger liar than us' and 'trist us, we are slightly more trust worthy than him' just isn't cutting it I'm afraid.
The only way it gets attention or traction is if opposition MPs, in every single interview, absolutely hammer the detail of every point and refuse to move onto anything further unless it's factual; it invites the interviewer to facilitate and press further which is problematic for a campaign built on 'Brexit means Brexit' because it's completely devoid of detail or meaning. If the interviewer is complicit or doesn't facilitate properly, then expose it as false or misleading and refuse to answer until the acknowledgement comes. But it relies on being incredibly well briefed and disciplined - which, unfortunately is not always evident in those chosen to represent the Labour Party in media appearances.
The other alternative is something like 'Brexit means Brexit' which can just be repeated ad nauseum until it becomes truth.