Lone child asylum seekers, some as young as 13, are still being placed in hotels despite the routine practice previously being ruled unlawful, the High Court has been told.

Every Child Protected Against Trafficking (ECPAT) said the proportion of unaccompanied youngsters aged under 16 being housed in hotels in Kent was “growing” with there being “no clear explanation as to why this is”.

The charity previously brought legal action against the Home Office over the practice of accommodating such young people in department-run hotels, claiming the arrangements were “not fit for purpose”.

In July, a High Court judge said the practice had been unlawful for more than 18 months, as the power to place the children in hotels “may be used on very short periods in true emergency situations”.

Mr Justice Chamberlain found that: “It cannot be used systematically or routinely in circumstances where it is intended, or functions in practice, as a substitute for local authority care.”

ECPAT also took legal action against Kent County Council, with the judge finding that the local authority was acting unlawfully in failing to accommodate and look after lone children seeking asylum when notified by the Home Office.

In a linked case, Kent County Council brought a High Court challenge against the Home Office, arguing it faced an “impossible situation” over accepting more lone young people while ensuring children already under its care were safe.

Brighton and Hove City Council also sued the department, arguing the practice of using hotels was unlawful.

After a hearing in August, Mr Justice Chamberlain ruled that the court should supervise efforts to address his findings, with Kent County Council and the Home Office required to “work together” in “remedying the unlawful situation”.

In written arguments prepared for a follow-up hearing on Friday, Martin Westgate KC, for ECPAT, said that unaccompanied asylum seeker children “have continued to be accommodated in hotels in numbers that have barely changed since the last hearing”.

“It is a cause for particular concern that a significant majority of them are under 16 and this appears to be a deterioration from the previous position,” he added.

Mr Westgate said Kent County Council was “still not fulfilling” its duty to all unaccompanied children, with there being a “significant inflow” of youngsters into Home Office-commissioned hotels.

The barrister said that one set of figures showed that since July 27, Kent County Council had not accommodated 185 lone children, of which 138 are aged under 16 and eight are 13.

He said two children placed in hotels had gone missing since the judge’s ruling.

Stephanie Harrison KC, for Brighton and Hove City Council, said in written arguments: “The continued unlawful use of hotels which is, in respect of under-16s, also a criminal offence, must be promptly brought to an end.”

She added: “No further children should be placed in hotels.”

Hugh Southey KC, for Kent County Council, said it written arguments that it continues to take “all possible steps to ensure that it is able to accommodate and support all unaccompanied asylum seeking children”.

He said “effective measures” had increased the council’s capacity, with some 777 lone children in its care as of September 8 – up from 466 on July 27.

As of September 6, the council had taken into its care almost 80% of unaccompanied youngsters arriving in Kent since July 27, he added.

The lawyer said steps taken include placing three or four children in rooms at a reception centre, using the support of an independent fostering agency and working with “semi-independent bed providers”.

But Mr Southey said the council “regrets” not being able take all children into its care, adding that there were “systemic problems” which could only be solved through Government help.

He said children the council had not being able to accommodate included 15 lone youngsters, 12 being over the age of 16, who require isolation due to suspected diphtheria.

The number of unaccompanied asylum seeking children in Kent was “constantly fluctuating”, the lawyer said.

Mr Southey said problems included “the lack of a properly functioning” National Transfer Scheme (NTS), where children are moved from one local authority to another to help even out the distribution of care.

Deok Joo Rhee KC, for the Home Office, said in written arguments that it was “reasonably confident” that a new funding arrangement with Kent County Council could be put in place by the end of October and that it had “not underestimated” the challenges the local authority faced.

She said “an immediate cash injection” of £9.75 million would help the council increase capacity, with the Government committed to bringing about “improvements to the speed of transfers” of children between areas which were a “necessary and important part of the solution”.

The lawyer said the Government was “alive to the need to ensure that the significant progress that has been made to date is not lost and that intensive efforts are maintained”.

She said that as of Wednesday morning there were 121 children in two hotels in Kent, with no children accommodated in hotels outside the county.

Mr Justice Chamberlain said he was still to give a ruling over Kent County Council’s legal challenge against the Home Office in relation to the NTS.

The judge said he would consider whether to make an order or injunction banning the Government from continuing to use hotels at a later date.

He said Kent County Council and ministers should agree a plan to ensure the local authority was meeting its obligations.