I can offer a very topical recommendation: I've not been to
Cambridge in yonks, but when I re-visit in May I'll be heading to the Champion of the Thames on King Street. Cosy and great atmosphere.
For anyone making a trip to
Sheffield, follow the river north-west towards Kelham Island, where you'll find the Kelham Island Tavern and the Fat Cat, two fantastic CAMRA pubs in a beautiful ex-industrial district where nineteenth century warehouses and factories and being joined by newer inner-city apartment developments. The Fat Cat is one of my favourite pubs in Britain - never less than a dozen real ales behind the tiny bar, and great pub food too. Last time I popped in for lunch I ended up staying for six hours.
In
Berwick-upon-Tweed, one of my favourite towns to stop at on the ECML, the Barrels Bar on the Berwick side of the old bridge is a cosy and popular local pub, which live music sometimes too.
Here in
Glasgow decent real ale pubs are hard to find (the locals preferring to cut to the chase with Tenants and fine malt whiskey

) but two atmospheric sixties timewarp boozers are The Laurieston, just south of the river on Bridge Street, ten minutes walk from Central Station and near Bridge Street underground station, and The Steps Bar on Glassford Street, five minutes south-east of Queen Street station.
Oh, and since the OP is a lover of the black stuff, the best to enjoy pint is (in my humble opinion) to get that SailRail ticket sorted and head to the John Hewitt on Donegal Street in
Belfast. Live music most nights and a lively and welcoming mixed crowd.