On Tuesday, 30 January 2018 22:48:09 UTC, jim wrote:
Net result is so far I can't fit both "feed" cables into the
terminals on the rear of the boost timer that I want to
replace

Fit a double outlet cooker plate adjacent?

https://www.tlc-direct.co.uk/Products/AA45DCOP.html

Fits on top of an existing flush back box and has 2 x cable clamps for the outgoing cable to the boost switches.

Owain