I found a link that may be very useful
https://www.electricalestimating101.com/estimating-tips/
I know that these tips are geared to US electrical contractors but there is a lot of relevance which UK electrical contractors could learn a lot from.
In the meantime, you may find another link interesting
https://www.countfire.com/blog/8-tips-for-training-a-new-electrical-estimating-apprentice/
Basil Wallace PgDip MIET EngTech