Spotting a pinball in the wild in England is still a fairly rare occurrence. Coastal (tourist) towns are possibly your best chance though, and ‘BrewDog’ bars usually have at least one.
I would recommend looking at www.pinballinfo.com which is a UK centric website and a good place to buy/sell machines and meet the locals. Also look at www.ukpinballleague.co.uk, which has details on signing up to your regional league
For the big annual shows, there is only one scheduled this year, but for the last few years it’s been the largest and arguably considered one of the best (though bias disclaimer - I am one of the organisers )
Andy Heighway’s UK Pinball Party was the dedicated pinball event, frequently with a guest speaker from the States along with a couple of decent WPPR comps. As of this year though he’s concentrating on getting Alien out of the door, so no party planned.
South Coast Slam was a sort of bi-annual-if-they-could-be-bothered event with a great mix of pinball and arcade cabs, but the organisers of that are still in their ‘taking a break’ mode sadly.
Northern Lights Pinball Show, still the biggest and the best. Takes place as part of Play Expo ( www.playexpomanchester.com ) over the weekend 8th & 9th October. We have discount tickets available through our website : www.ukpinball.com/twilightzone . We (Northern Lights Pinball) run this as a non-profit, so by buying directly from us you’re saving a few quid and helping our contribution to charity (we support Teenage Cancer Trust). This is the closest we get to something like ReplayFX. A huge arena filled with hundreds of arcade cabs, over 100 pinball machines and just about everything else gaming related (CosPlay, PlayStation, Xbox, retro consoles and so on)
There are a good deal of smaller competition based events too, but rather than list them all you’d be best looking through the list at http://www.pinballnews.com/diary/index.html
For small venues that are open year round, again you’re probably best looking through Martin’s list at http://www.pinballnews.com/sites/#uk . Most of those are based around the South of England, so he’s probably missing a few further North. From a quick scan the only ones I think missing and worth a mention are http://www.specialwhenlit.co.uk and www.arcadeclub.co.uk which with around 20 pins each are probably the largest permanent collections in the UK