A travel document is for people that need a visa for Canada. They have to be able to show either a valid PR card or PR Travel Document to be able to board the plane.
You are visa-exempt, so you can board the plane just on the strength of your passport, like a tourist. Do not state at the UK airport that you are a PR, as they may not let you board without seeing the proof.
I just wanted to update all those who followed the posts,
I have finally contacted the Immigration dept in Canada through back channels and they have advised that My immigration status is fine and still active -( so long as i Accompany a canadian overseas)
I just need to apply for a new PR card.
This is Great news and I am thrilled and would like to say a Massive thanks for all those who supported the post and replies!
Thanks to CanadaVisa for this amazing support as we navigate through the complex and stressful world of Visas.