I’d purchase a fleet of old double-decker Blackpool trams, and modify them so they could all be capable of running on the national rail network. I’d install Fainsa ‘ironing board’ seats but keep everything else original because they are nice trams and they deserve to keep their heritage.
I’d run one route only, and that’d be from Kinbrace to Lake (IOW). The calling points would be as follows:
Kinbrace | Altnabreac (double back) | Kinbrace | [ into Inverness and back out immediately without stopping ] | Dalwhinnie | [ 5 hour 43 minute halt on the Forth Bridge to admire the view ] | [ into Edinburgh and back out again without stopping ] | Breich | Uddingston [ 2 hour 16 minute stop to allow passengers to visit the Tunnock’s factory ] | [ into Glasgow Central and back out again without stopping ] | Kilmarnock | Auchinleck (double back) | Kilmarnock | New Cumnock (double back) | Kilmarnock | Kirkconnel (double back) | Kilmarnock | [ via the Settle and Carlisle line ] | Crossflatts | [ Leeds to York via Church Fenton without stopping ] | [ around the Harrogate loop ] | Hornbeam Park (where the train will divide) - [ the tram will split in half and only the front half will continue onto Lake whilst the other half reverses back and terminates at Harrogate ] | [ into Leeds and back out again without stopping ] | [ full speed down the ECML ] | [ through the Thameslink Core ] | Guildford | [ full speed down the PDL ] | [ not stopping at Portsmouth Harbour - straight onto a specialised ferry with train tracks onboard - and onto the IOW ] | Smallbrook Junction | Lake (train terminates)!
This route would run once every 7.5 days and it’s estimated to take between 2-3 days.
Below is a hand-drawn route map. I would do it on some sort of sophisticated software, but unfortunately I do not have access to which.