If a local planning authority decides that your application is invalid, it should let you know the reasons in writing, or if there is a simple solution, telephone or email you. More information is available on the Planning Portal, invalid applications.
If you can’t resolve your dispute with the local authority there is a procedure set out in Article 12 of the Development Management Procedure Order to resolve such disputes. The applicant can serve a notice on the planning authority saying what additional information which has been requested is considered unreasonable and why it is considered unreasonable and requesting that the requirement be waived. The planning authority can then serve a notice that it no longer requires the information called "a validation notice" or one saying the information is still required, "a non-validation notice".
After the statutory time period for determining the application has expired, the applicant can appeal against non-determination (this is basically the same procedure as if the application has been refused). In considering such an appeal the inspector will consider both the dispute regarding invalidity and the merits of the application itself (though if the Inspector considers there is insufficient information to allow the appeal it will, of course, be dismissed). The Planning Practice technical guidance website provides more detail on delays in the validation of an application.