This is the end, beautiful friends, the end. Hand of God has struck the hour, and the Christmas lights along Highgate Road reflect in beads of grease that cling to the meaty petals of the small doner kebab in my palm. The romance. It's remarkable that 20-odd years down the line and with an impressively heavy legacy in tow, the impending dissolution of Cathedral seems rather hasty; most bands have essentially outstayed their welcome by this point. This wistfulness is no doubt fuelled by the vitality and imagination of 2010's The Guessing Game, which is the work of a band at a creative peak, rather than struggling for ideas. Well, they've decided to quit while they're ahead; next year's 'The Last Spire' will be the final output before they head for cloisters new.

Doom acolytes file into the Forum in droves for this send-off and the 2,500-capacity theatre is close to full if not a sell-out. I thought the swansong may have been a circle-closing blowout in Coventry or Birmingham, but this venue is the kind of grand crucible the occasion deserves. We arrive in time to take a fuel stop (pintwatch: £4.20 – ouch!) and catch special guests, Stockholm's Grand Magus. This is a band that recognize that the iconic metal song doesn't need much tinkering to stay fresh; they don't try to pastiche it, chrome gloss it, nor bury it in sludge. They capture the imagination by doing traditional things better than others: The riffs are heavier, the fast bits more incisive, the vocals peerlessly metal. We get 40 minutes of stirring tankard-clankers like “Hammer of the North” and “Iron Will” which draw as much from Dio-fronted classics and early speed metal as the 'stoner/doom' touchstones they often get lumped in with. The crowd pump fists and bang heads like the days when this was truly outsider music.

A blast of Budgie during the interval subsides and a reel of clips from obscure horror and films leads us into the frazzled groove of 'Vampire Sun'. A boulder-dragging 'Stained Glass Horizon' immediately keeps the foot firmly on the throat. They maintain this ruthless momentum throughout and play it pretty straight for 90 minutes, with little by way of banter, fanfare or standing on ceremony. I don't know what I was expecting; guest appearances, new songs, melodramatic tearful goodbyes, stage invasions and equipment dismantling? Don't get me wrong, this is a brilliant Cathedral gig; it just feels more like an exclamation mark than a full stop. It certainly sounds fantastic. Gaz Jennings is an underrated guitar pioneer; a riff alchemist and master of tone. It fairly rips out of the PA tonight, a punch in the sternum with added crunchy topping. Lee Dorrian's shamanic incantations still manage to cut through and stir up merry hell.

Amidst all the bouncing, charging lynch mob anthems, 'Cosmic Funeral' and 'Ebony Tears' slow things down to an agonising lurch, and it's mind-bendingly great. Cathedral conquered this style early on and moved on, but they still sound as brutal as anyone who tried to follow in that crawling slipstream. First encore 'Corpsecycle' demonstrates how they successfully embrace thrashy melody while staying at the uncompromising extremities of heavy music.

“I'll miss you lot; but not half as much as you'll miss me. For I am Matthew Hopkins, Witchfinder.” One final magic carpet ride and it's over, nothing to do but set a cig crackling into life and make a dash for Kentish Town tube station with a slim hope of making the last train. Farewell Cathedral, a band who left their mark and followed what they loved. That fact will echo through the universe for eternity.