Right now my quandary is the train luggage allotment...
George, one solution might be to rethink your load and take much less cargo and luggage. The UK has many shops for food resupply and despite a good possibility of rain, you'll be traveling at a warmer time of year....
My trip a year and a half ago (part in USA, part in Ontario Canada), I anticipated warm weather, I wanted to be able to bike in rain without rain pants. For that trip I brought sandals to wear on the bike to keep my bike shoes dry in rain. But this trip, I am assuming if I am biking in the rain, I will be wearing rain pants. And that means rain covers for my bike shoes. But will probably bring sandals, just in case, it depends on my weight when done packing. Third photo, the sandals I biked in on rainy days on that trip, that trip was on my titanium bike. They have a stiff enough sole I can ride all day without foot pain, but I need the right pedals for those sandals to work well.
When I went to Iceland, I only took one jersey, it was long sleeve. I checked out the weather averages for this trip, I am leaning towards one long sleeve and one short. Otherwise, pretty much teh same clothing as I took to Iceland. But I might bring one short and one sleeve shirt instead of two long sleeve. For biking, am leaning towards two pair of bike pants, one would be shorts and the other would be long pants that convert to shorts. That is what I used in Iceland.
I always bring a down vest and stocking cap on trips. Even if it gets quite chilly, a rain jacket (in dry conditions) over the vest is almost as good as a winter jacket. I looked at the June data for London, Leeds, Edinburgh, and John O Grotes on:
https://weatherspark.com/m/147876/6/Average-Weather-in-June-at-London-Heathrow-Airport-United-KingdomWhere possible I always look at airport weather data since they have the best data on the past for averages and statistics.
I do not recall where i heard this, but I heard that Scotland can be buggy. I plan to treat my clothing with Permethrin and also bring insect repellant. Not sure if I will have a head net or not.
First attached photo is my Nomad Mk II and my Ortliebs, plus handlebar bag. This would be what I bring on this trip. The Rack Pack (31 liter duffle on top of rear panniers) would be close to empty with no food. I do not see myself cutting back much on my load. And I was thinking that I would buy very little food before I get onto the train to make sure that I do not start out with too much weight and bulk. At the time I took this photo, I had not yet learned how to correctly attach Rack Pack with Backrollers.
I have both Carradry panniers and also the Ortliebs. At this time, planning on the Ortliebs, but might change my mind on that later. Second photo, Carradry in back on my Nomad. The Carradry are about 25 percent larger than the Ortliebs but weigh about the same. If I brought the Carradry, would bring a dry bag for the rack top bag.
I have a Carradice Camper, bought it a few years ago. One day I noticed that the US Dollar was unusually strong, tried to figure out if there was anything that I might want some day, bought the Camper at that time. I have not used the Camper yet, but I figured if I ever did a credit card tour, I would use it then. I like the 31 liter Ortlieb, it attaches on the panniers very well, mine weighs 795 grams. I have not weighed the Camper, the Nelson Long Flap is 1025 grams. How to correctly attach Rack Pack with Backrollers at this link:
https://www.youtube.com/watch?v=OtxsoOa2h48If I decide to bring the Carradry instead of Ortliebs, I will consider the Camper. I used a Nelson Longflap on my Pacific Coast tour, but buckling and unbuckling it from my bike every day was a lot less convenient than the Ortlieb Rack Pack.
I have a few other ideas for carrying my luggage in the train station, but it is all contingency so I won't elaborate here. My plans are to start planning with worst case scenario, and later if I find something smaller and lighter will work, do that instead. But plans start with stuff that I have certainty will work, modifications come later.
At some point I will be trying to remove one or two more pounds (or kg), but that step comes last.
I am assuming food will be readily available south of Leeds, but once north of there I anticipate carrying more food with me, especially north of Edinburgh. I probably will bring a few days of food from home, in original store packaging, this would be lighter dehydrated stuff that might turn into contingency foods later in the event that I don't plan my grocery shopping well enough.
The part that I think will be hardest is that for my 72 years of existence, all driving is done on the right side of the road. My helmet mirror is on the left side, it can't be changed. So, I bought a mirror that attaches to eye glasses so I can try to put that on the right side of my head.