Councillors have agreed that additional funding should be allocated to four flagship projects to support children with special educational needs and disabilities (SEND) in Hertfordshire.

Collectively, the county council has already allocated more than £50m for the four schemes – in Croxley Green, Hemel Hempstead, Potters Bar and Letchworth Garden City.

But on Monday (July 21) it was reported to a meeting of the council's cabinet that, without further funding, the schemes "will not be deliverable".

Members of the public were excluded from the part of the meeting that considered the exact amounts required.

But when the public part of the meeting resumed, councillors agreed that the additional funding – referred to at one point as a "multi-million pound additional bill" – could be allocated to the projects.

And, in the wake of the escalating costs, they also recommended a review of processes to reduce the risk of a recurrence in future.

The four projects to be granted the additional funds include the relocation of the Breakspeare School to a site in Croxley Green and the creation of a satellite site for the Collett School, in Hemel Hempstead.

They also include the construction of the planned Journey's End school for children with communication needs and autism, in Potters Bar, and the relocation of the North Herts education support centre, in Letchworth Garden City.

Presenting the proposal executive member for education, SEND and inclusion, Cllr Mark Watkin, highlighted his own "deep concerns" about the reasons for the additional expenditure.

But he stressed their commitment to completing the projects "in spite of the failures of the previous administration".

Accounting for the increases, he pointed to higher-than-inflation increases in building costs, as well as a failure to make a correct application to the DFE.

In the case of the Breakspeare School, he pointed to a failure to identify "significant additional groundworks necessary to address the chalk infrastructure".

Cllr Watkin said that it was the scheme at Breakspeare – that will deliver an additional 113 "desperately needed" places for children with severe learning difficulties – that had caused "greatest concern".

Although acknowledging it was "the most significant and complex SEND project in terms of size and scale", he said he was concerned that some of the issues might have been identified sooner if there had been a more detailed ground survey.

"The fact is, this is on chalk land and because of what has now been discovered, we're going to have to build substantially deeper foundations to make sure that the buildings are absolutely secure and solid," he said.

"But once built, it will be a school for many generations to come."

He said that five other potential sites had been reviewed as part of this process.

But he said he had been advised that risks associated with these alternative sites were unknown and could be as high as this one.

He said moving the scheme to an alternative site would delay the provision of the SLD places.

Executive member for resources and performance, Cllr Chris Lucas, said that he was at a loss to understand how they were in a position whereby surveys were conducted, but then they discovered "a disproportionate amount of chalk" that would impact the budget.

Adding: "So I do need to ask questions around what kind of procedures we have in place.

"What contractual arrangements do we have in place with those who perform those surveys on our behalf? And whether or not there are some competency issues there?

Cllr Lucas also questioned when the last administration knew of this, and whether they "had kicked it into the long grass" for the new administration to pick up.

He asked what safeguards could be put in place for large-scale builds in the future "to make sure that we're not caught in this situation again".

In response to the concerns expressed by councillors, deputy chief executive Scott Crudgington pointed to past successful schemes – but committed to undertaking a review.

He said: "The approach that we take to site selection – and then the preparations for schemes like this – has followed all due processes that have normally been followed in the past and have delivered many successful schemes as well.

"However, the point being taken s that whether there needs to be improvements in the process to try and mitigate risk further […]

"This has been a second site identified in recent times as having issues below the ground, once we have got underway with construction.

"I absolutely will take the view of the cabinet today. And we will undertake a review to see what parts of the processes need improving to try to reduce those risks going forward."