Update on this topic....
Yes I eventually used the spare fuse socket(engine compartment driver side) above the deicer socket as the piggy back was stopping the fuse assembly cover from closing. Put in a 20A fuse. I ran the new circuit wire from the assembly through to wheel arch area and came up underneath the driver floor through a grommet below the thick padding on floor. From there, I split the wire into 3 separate wires with 10A,5A,5A fused lines to allow for 24hr surv dashcam , sat nav , and spare for lighter socket for future separate parking camera/monitor. Tested all working for a few days already. No deteriment to engine starting even with 24 hr surv camera working.. Thanks everyone for your advice and contribution. At a later stage I will source suitable toggle switches for neater installation. ps. I did not involve the glove compartment or the central console panel. ..Overall, I am grateful for all the encouragement and help to pick up a completely new skill from learning how to use a test meter,identifying fuses, understanding their limititations, testing for soundness in installation, routing circuit from engine area to driver footwell, correcting a badly wired addon from seller and to cap it all , I saved over £300 by not asking the local car security specialist. Well done and thanks to this community. Keep your ideas coming..Thanks again