Its scripted to fuck. For a starters Bamber would just say he would be killing the family, at a push mention his methods. She says stuff like " how he would say goodnight to everybody " Bamber wouldn't say that. It's an add on by Julie or perhaps EP.
Also he
The excellent memory for dates. She would simply just say " he's been talking about it for a while, her recalling Xmas 84 and January 85 whilst maintaining a heavy schedule in her own life and at the same time being " flippant " of what Bamber is saying doesn't reflect the true picture she'd be able to recollect precise dates. Nobody would. Everyone is too wrapped up in their own affairs. Me, you, Mr Jones at number 10. Accept it may have come at prompting from the coppers. But it's not a true picture of what Julie is remembering.
It's possible because all through those last months he was keeping up appearances in front of everyone, following his return from the round the world trip. He even managed to fool Nevill, who told John Seward he was pleased that his son was finally shaping up to farming.
But we know subsequently that his motive was to align with the terms of Nevill's will, and not from some genuine interest in the agricultural industry. It appears Jeremy managed to pull the wool over everyone's eyes, save farm secretary Barbara Wilson, who speculated that there was an ulterior motive in everything he did.