JCT: Does an acceptance of extension of time and acceleration automatically mean an acceptance of the associated costs.

I am involved in a project with a public client, where the design team underestimated the scope & quantity of work.
I was asked send on a revised programme along with any associated costs that would be required in order to accelerate the project bringing it in as close as possible to the original date, which in this case is within 2 months from the original handover date, which will require double shifts and weekend working.
The contract administrator asked for costs prior to a formal request for the extension which were duly given, and made an “offer” of half of the figure requested., without any justification. When asked they have simply said it was a “trade”.
The CA then waited to the weekend before we were due to step up the workforce for the acceleration and said "we accept your programme for extension of time but do not accept the costs. "
I was wondering ;

1, Are we duty bound to proceed with the acceleration.
2, Does the acceptance of the revised programme and extension of time go hand in hand with the costs (that were previously provided) and deem to be automatically accepted.
3. Should we just revert to the original programme and extend the completion date to reflect the increase in scope of works.

Any other avenue possible?

Thanks in advance.

It doesn’t sound like the Contract Administrator has been adhering to the contractual mechanisms. You don’t mention which JCT contract you are on so I can only deal with the principles.

Before getting into acceleration you should have had an extension of time for the increased scope of work otherwise you are being asked to achieve practical completion before the original contract completion date.

However, ignoring this point, the Contract Administrator does not have the power to force you to accelerate or to negotiate the quoted amount so to answer your questions:

  1. No.
  2. Extension of time should have been dealt with before acceleration and under the relevant provisions of the contract, they are separate concepts with different rights and obligations. The Contract Administrator should have either accepted or rejected the cost and time included in your acceleration quotation, they do not have the power negotiate, assess, impose or deem your quotation as accepted.
  3. Yes if the quotation was not accepted then you proceed as you would have and work to a later completion date for which you should have an extension of time with costs.