Once a request for mutual legal assistance has been agreed by the Home Office then that assistance should be provided by those given the job. The job was to ask certain people certain questions and record their answers. It wasn't to have pre-interview discussions with the witnesses. I can imagine the fuss if it was discovered that the PJ had off the record discussions with the people OG wanted interviewed in Portugal. In my opinion that would have been seen as highly suspicious and irregular.
I'm not quite sure how that fits into the topic thread of translation errors...
Are you saying that LP shouldn't have used the UK police's years of experience in eliciting information in the least stressful manner possible while the opportunity was there? And that they shouldn't have used the invitation offered by the PJ to feel free to ask any other questions that they deemed potentially useful?
The "off-record" (informal) chats could have been over a cup of tea, introducing themselves, getting their full contact details, putting them at ease and whatever else.
Many may have been pissed off at the PJ "leaks", general handling and may have wanted to blow off a bit of steam prior to the official recordings. In the general interest of diplomacy and avoiding OT rants in the official recordings, there may have been a good reason to let them let off a bit of steam beforehand, IMO.
And it's not clear from the rogs whether the PJ officers were also able to listen in to the "off-record" chats in any case - perhaps they were, perhaps they weren't.