There is a lurking doubt whether they could consult on the 299 project then submit the 1200 one to yourselves. Am I right thinking that once they have started the statutory consultation process they are bound to submit to you the proposal on which they have consulted?

Before submitting an application to the Planning Inspectorate, the applicant is required to carry out extensive consultation on their proposal.
This involves providing information about the proposed development to various statutory and non-statutory bodies, as well as the wider community to gain information and feedback that can help in shaping the proposal. For example, where the application is larger and more complex, applicants are encouraged to go beyond the statutory requirements of the Planning Act 2008 (as amended) and carry out several stages of consultation.
The length of time for the applicant?s pre-application consultation will vary depending upon the scale and complexity of the application. The applicant will usually carry out number of non-statutory pre-application consultation stages in order to inform the proposal before starting its statutory consultation on a more refined development.
Once the application is submitted the applicant must demonstrate in its Consultation Report document which is submitted as part of the application documents, how the proposal progressed as a result of both statutory consultation as well as non-statutory consultation.
As you have noted, the applicant must therefore carry out its statutory consultation with local communities including local planning authorities, relevant statutory organisations and members of the public. Before starting its statutory consultation with the local community under s47 of the Act, the applicant is required to prepare a Statement of Community Consultation (SoCC) and carry out their consultation as set in that document.
In their SoCC, the applicant should clearly describe their project and its scale and refer to both benefits and the impacts that proposed development would on the local community.
The SoCC should also indicate what information will be provided during the consultation process on the scope for any associated land restoration, landscaping, other mitigation or compensatory measures for natural habitats impact.
The description of the proposal must be clear during consultation, should the applicant make any changes to its proposal following its statutory consultation are encouraged to carry out further consultation (see DCLG: Guidance on pre-application process available from the link below).
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Pre-application consultation therefore, whether it is non-statutory or statutory, is the best time to influence the proposal and provide the developer with suggestions about how the impact of the project could be mitigated.
Once the application is submitted to the Planning Inspectorate, the 2008 Act process lays down a strict timetable. It is not normally possible for substantial changes to be made to an application once it has been submitted.
Summarising the above to answer your query, the applicant is encouraged to carry out both non statutory and statutory consultation in order to shape their proposal. Moreover, the applicant is encouraged to carry out their statutory consultation on the most refined option that progressed as a result of its consultation. Moreover, once the application is submitted for consideration, no substantial changes to the application are allowed.