Asking for more time on application

Is there a best way to ask for more time to complete a PIP application? Do they accept a request by text or must it be written and posted? What grounds for time extensions are they likely to consider? The person concerned was thrown into such manic anxiety when the forms arrived that he was suicidal and decided not to do them then for fear it would totally push him over the edge. Friends have since encouraged him to continue with the application, and get him some help to fill in the form, but time is now short to do this and gather together the evidence. His form is meant to be returned by 1st Sept but it would be useful for him to see his GP first and earliest appointment is 5th Sept.
All advice gratefully received

Hi Terry,

A 2 weeks extension for PIP is usually given without any problems. This is one time when I would suggest that you don't put it in writing as things can take 3 weeks to get through the internal post system. Phone and ask - as I say, legislation allows for an extension of 2 weeks.

Yes ring them and ask for an extension. I was granted a two week extension because I needed time to get advice from my local Citizens Advice.

I rang and got mine, no problem!

Thank you all for this advice. Will ring today