Migrants are "often among the exploited, the rejected and the vulnerable, fleeing from war and civil disturbance, extreme poverty and terrorism", according to the Roman Catholic Archbishop of Southwark, Most Rev Peter Smith.

Speaking at St George's Cathedral during its annual Mass for Migrants yesterday, Archbishop Smith warned of the danger faced by young people in the world's poorest countries from traffickers.

He added: "Nor can we close our ears and eyes to the dreadful tragedy over recent months of hundreds of migrants drowning in the Mediterranean, fleeing from persecution and abject poverty and heading for Europe in over-crowded and unseaworthy boats."

The Archbishop also highlighted the plight of those who arrived safely in the UK, referring to the recent report of the all-party parliamentary group on migration, which found serious weaknesses in Britain's detention and removals policies. The current system is "seriously detrimental to the individuals who are detained in terms of their mental and physical well-being, effectively stripping them of their human dignity and respect", the Archbishop said.

He added that there were "no easy answers" to the problem of how to balance the needs of resident citizens with those of migrants. However, he said, "We must pray for our politicians and our government, both national and local, and whilst we have the right and the duty to hold them to account, we should always do so with courtesy and respect."

The Mass was attended by ambassadors from Libya, Ethiopia and Lithuania, Simon Hughes, who has served as MP for Southwark and Bermondsey for many years, former MP Sarah Teather who led a campaign to stop the detention of child refugees, and mayors and councillors from around London.

Music was played from Cameroon, the USA, Australia, Slovakia, China and Uganda. Languages used in the prayers, led by pupils from Notre Dame RC Girls' School, included Tamil, Tagalog and Yoruba.