I'm going to list a few other candidates for the UK's biggest problem:
* The pound plummeting like a rock.
* Xenophobia, bordering on fascism, being advocated by the press.
* The gradual, quiet, handing of the NHS to private companies.
* Ever growing demand for food banks, most notably by people working jobs that don't pay enough to fulfil basic needs.
* The only vaguely viable opposition to the government self-destructing right when they're needed most.
But sure, its definitely people complaining that are the problem.
* Xenophobia, bordering on fascism, being advocated by the press. - BBC is nothing but a continuous charity appeal.
* The gradual, quiet, handing of the NHS to private companies. - Precedes Brexit.
* Ever growing demand for food banks, most notably by people working jobs that don't pay enough to fulfil basic needs. - Precedes Brexit.
* The only vaguely viable opposition to the government self-destructing right when they're needed most. - Precedes Brexit.
Completely off-topic.
These things are still:
>"candidates for the UK's biggest problem"
Brexit doesn't give £350m to the NHS. Brexit doesn't get us out of ECHR (and that wouldn't be a benefit anyway, since ECHR agrees with UK on over 99% of cases). Brexit doesn't give us control over our spending. Brexit doesn't give us control over immigration.
Are you suggesting that "remainers being negative" is causing lack of confidence. That puts the cart before the horse somewhat.