Very interesting summary of the future development of the new UK Tentative List and the specific case of Port Sunlight.
I noticed that 3 of the sites that you mentioned are indeed in Merseyside (Port Sunlight, Birkenhead Park and Sankey Viaduct) and correspond to a timeframe (19th century) from which part of the OUV of Liverpool came from, although of course with a verydifferent flavor: I consider the first public park in the West and the revolutionary early 19th century viaduct are indeed very outstanding and that the planned town, using the thematic angle that you mentioned, could arguehaving OUV.
It would be interesting to see sometime Ebenezer Howard's Letchworth and Welwyn garden cities, extremely influential in the history of urban planning, go for a TListing at least.
I also see there may be an angle for postwar Modern Movement Sites in the UK, like the Barbican (although criticised, it was very revolutionary, vast, influential and for the most part, succesful), Ralph Erskine's Newcastle Byker Wall (portraying a break with the brutalist and functionalist social housing of previous decades, experimenting approaches that have reverberated in the following decades, towards more community-oriented housing) and James Stirling's Leicester Engineering Building, Cambridge History Faculty and St. Andrews Andrew Melville Hall.
(and St Helena / Turks and Caicos if they reapply)[/quote]
British Virgin Islands
Of course, sites in overseas dependencies, colonies and associated territories have provided a rich field for inscriptions for countries as France, the US, Australia, New Zealand, the Netherlands, Denmark and the UK and I think they help (even when located mostly in some countries with a high number of WHS) to expand the distribution of WHS around the world. I personally don't even count oversea territories sites that are outside of Europe, as "European sites" as UNESCO does.
As I said sometime before, very much in favor of it, even when being in a crowded and highly represented field of already inscribed European sites. I think (as it was the case with Albi and the Mantua component of Mantua & Sabbioneta, in this category), it just stands from the crowd.
Would like to see sometime Oxford and Cambridge sometime vye for a listing.