Ok guys update.
I bought an 18w charger with Apples USB-c to lightning fast charge cable.
I also got my multimeter and did tests on my current charger with third party “3 in 1” cable and it was crap. I was getting about 2.5w (5v 0.5a)
my 18w charger is giving me about 12.5w of charging power at 21% battery. Though I did note it was charging slower on an older 4 gang extension lead I had only giving me 1a
I’m not sure if this is the highest charge rate an iPhone will charge at. I’m deffo not getting the 18w anyway but I can definitely cope with 12.5w (5v 2.5a) as opposed to my pitiful 2.5w charge.
I was using the old style apple power adapter that only gives out 5v 1a.
hope this is interesting to anyone.