Britain has been accused of adopting a "xenophobic response" to the migrant crisis by the UN's special representative on international migration.
Peter Sutherland urged Britain to join the common European approach towards migrants, saying any country that thought it could stop the "alleged floods" of people with fences was "living in cloud cuckoo land".
Mr Sutherland told BBC2's Victoria Derbyshire programme that Britain received a small number of migrants compared to other countries.
The first thing we have to do collectively is to deal with their conditions.
Instead of talking about sending Gurkhas or building fences, we should be thinking of the humanitarian crisis.
A joint police operation has been launched to target people-smugglers who profit from the desperate migrants trying to reach the UK.
Calais' Mayor has accused Cameron of treating the region with "contempt" - and called on authorities to open the border unless help is given
More fencing and extra sniffer dogs have been sent from the UK to Calais in a bid to curb migrant incursions into Britain.