In the event of wet weather, I'd use...
A decent rain jacket (
Giro Neoshell)
A base layer (
Brynje Super Thermo)
A
Torm smartwool jersey if it's colder
shorts to suit (I use touring baggies - Rohan or Aldi, with regular M&S undies)
Goretex waterproof shortsSPD sandals, no socks.
A goretex cap (baseball style, the better to keep rain off my glasses)
The Neoshell jacket cost me £35 in a Bike Nashbar clearance sale, rather than the £300. I've come to the conclusion it's better than eVent, and is just about breathable enough to use as a windproof layer on a dry day, provided I don't work too hard.
Gore Shakedry is likely as good or better, and certainly better in terms of long term water beading, but it's downright delicate. If you fell off and hit the road it would be a write off, and something like a briar or bramble dangling from a tree over a cycle track would probably rip it too (DAMHIKT).
I like the "string vest" baselayer. It soaks up very little water, dries very quickly, and does well at temperature control.
Waterproof shorts is because you get just as wet from sweat in full length waterproofs as you would from the rain, you want something to fend off the rain running off the bottom end of your jacket, and I've come to the conclusion that rainlegs are only up to a short-ish commute.
Bare legs and feet is based on skin being both waterproof and fast drying. Trying to keep legs and feet dry in a touring context is also pretty much a lost cause.
The basic rule with SPD sandals is that if you don't need long fingered gloves, you don't need socks. In fact, my toes do a little better than my fingers do. I generally take a pair of wool cycling socks and a pair of goretex socks, just in case, but I've not needed them on tour yet. They save on carrying extra socks and evening footwear too.
If you've been riding all day in the rain, most of what you are wearing will be at least damp. If it's still raining the next morning, put your damp stuff back on. If you put on dry gear, it will be just as damp as yesterday's damp gear in a fairly short while, and you'll soon end up with nothing but damp cycling stuff to wear, which is somewhat galling on a dry day.
The northern end of Scotland will be distinctly cooler than England. Last time I went (mid June), there was a persistent north-easterly wind that kept the temperature down to 10 or 12°. Make sure you've some suitable clothing - legwarmers and a long-sleeve jersey at least, and windproofing.
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I like gilets. They are very good at keeping you fairly comfortable, but rainwear they aren't.
I remember the Elenith one year. I left Rhayader in short sleeves and a gilet, in the sort of light drizzle that's not worth caping up for. The drizzle increased very sneakily, so by the time it was precipitating enough to warrant waterproofs, I was already wet through, so I just carried on rather than stopping. Going over the top by the Forest Inn was proper rain, combined with sleet and hail. The rain stopped about by Kington, and by the Kingsland control (near Leominster) I was nearly back to dry.
