Mid layer...

[Teflon Jnr]

Keiss heated vest works bloody wonders last year on the way to dover I rode for nigh on 100 miles with my jacket unzipped and hadn't noticed.that morning it was bloody freezing but those vests are unbelievable

[Toe]

I usually have a poly sports t-shirt as my base layer, mid layer is an old Tog24 thin fleece, a minimal insulated jacket, and then bike jacket on top.
Got to love being able to layer as required.