There are some online Fitting calculators. I'd use these to work out your size, find a similar sized bike in Evans, then go and test ride.
Imo it's quite common for people to go for larger frames than they need for their first bikes, 1) because most sizes reference the seat tube and 2) the simple Evans size guide is a bit on the large side.
BioMechanical Cycling v.8
mediafire.com/?5xnxnyynzih
...and his WW page, with more info is here: weightweenies.starbike.com/forum/viewtopic.php?t=51071&sid=c66b95baef28bc3a1c8bbc8e319d185b
Competitive Cyclist Fit Calculator
competitivecyclist.com/za/CCY?PAGE=FIT_CALCULATOR_INTRO
There are some online Fitting calculators. I'd use these to work out your size, find a similar sized bike in Evans, then go and test ride.
Imo it's quite common for people to go for larger frames than they need for their first bikes, 1) because most sizes reference the seat tube and 2) the simple Evans size guide is a bit on the large side.