Migrant children are being detained at airports in inadequate conditions – without fresh air and natural light for more than a day, according to a report.

The Independent Monitoring Board (IMB) for London Heathrow and City airports said better facilities were needed for people put in holding rooms for long periods and overnight.

The body – made up of volunteers appointed by ministers to detention centre conditions – looked at the treatment and welfare of people in detention at the two airports and immigration reporting centres Becket House, by London Bridge, and Eaton House, near Heathrow.

Provision at Heathrow airport was “adequate” for short periods of detention “but, without fresh air or natural light, is unsatisfactory if the stay extends more than a few hours, especially for children,” according to the findings.

Out of almost 17,000 adults held in the airport’s detention rooms between February 2019 and January 2020, 2,145 people were kept in the facilities for eight to 12 hours.

More than 1,000 were held more than 12 hours, with 134 kept for more than a day, the report said.

Almost 2,000 children who were alone or with families were detained in the facilities during the same time period – 73 of which had to remain in the conditions for more than 12 hours, while 14 were held for over 24 hours.

The accommodation at City Airport was “excessively cramped” and the rooms at the two reporting centres were often overcrowded due to “unnecessarily long waits” for transport to detention.

The Board also raised concerns about detainees not having access to their own medication, which “inevitably puts their health and wellbeing at risk.”

Although the Home Office is now addressing this, the report said the Board is “still very concerned about the present situation and the amount of time taken to reach a solution”.

There were also difficulties in detainees at airports accessing legal advice, with the IMB claiming: “The services purported to be accessible through an advertised phone number are non-existent.”

IMB chairman Angela Taylor said: “Overall we have found many detention and escort staff to be caring and sympathetic to the detainees they have to manage, including vulnerable individuals and families.

“However, detention is often an isolating and uncomfortable experience, especially for those individuals who are waiting for long periods, are tired and anxious after their flights, and in some cases are fearful of what will happen to them if they are sent back to their own country.”

A Home Office spokeswoman said: “Detention is an important tool in the immigration system but it vital that it is carried out with dignity, respect and protects the most vulnerable.

“As this report recognises, we have already made improvements, particularly in relation to managing detainees with mental health issues.

“We will continue to look for ways to improve detention, for both the care and welfare of detainees and our effectiveness to enforce removal from the UK of those who do not have the legal right to be here.”