Hi Pennyy
Not to put it too strongly, what you read is utter nonsense. There are plenty of people who don't use the freepost system. Do the DWP like it? No, because it means they have to sign for submissions, and they can also blame the claimant if the form gets lost and claim it never arrived. However, if you send it through tracked post, they will still sometimes claim it didn't arrive, and that's when you say, you have proof it was delivered and signed for. Please don't worry about it - you did the sensible thing which thousands of other people have done. A PIP claim has never been turned down because a claimant used tracked post.
BIS
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