Al Murray, Royal Albert Hall

You may have thought that the Brexit vote in June would have been manna from heaven for Al Murray as the Pub Landlord, his knucklehead xenophobe creation.

But in this uneven and – at two-and-a-half hours – overlong show, the referendum result and what it means for this country is mentioned early on but is hardly the focus of the show.

And that's an enormous shame, as Murray's recent shows have put politics front and centre of his act to great and rejuvenating effect for a character that had, for me at least, long become stale and predictable.

Let's Go Backwards Together augurs well in this respect at its start, even after rather too much banter with the audience – most of it throwing up little in the way of off-the-cuff humour and only the occasional cruel and funny putdown – as the Pub Landlord (incorrectly) tells us we are in the 20th week of “Great British Freedom from Brussels".

Part of the show's lack of oomph may have been due to the large venue – but then Murray made surprisingly little use of the Hall's associations with the musical bombast of the Last Night of the Proms, or the annual, deeply respectful Festival of Remembrance – two very different but Union flag-bedecked events that the Pub Landlord would surely approve of wholeheartedly.

Rather this is a meandering entertainment, with songs (performed with the onstage band) used as lazy fillers, and a long list of targets for ironic despatches (an irony that still, after all these years, some of Murray's fans seem oblivious to) on Isis, Muslims, Donald Trump, driverless cars and airline crashes, as he longs for the Britain of 1955 – post-defeating the Germans, pre-the debacle of Suez. Theresa May does, though, get a deft mention – “We've got a woman in charge. Don't cheer, sisters, look what happened last time.”

Yet Brexit and its consequences for UK politicians disappears altogether from the show in the second half. The Landlord even appears to suggest he didn't vote in the referendum – an astonishing fiction, surely, but one that allows Murray not to deliver the Brexit position from this most proud flag-waver. The lack of triumphalism is noticeable – which leads me to wonder if Murray has gone as far as he can with this character after more than 20 years of his ridiculous “patriotism”.

But when Murray does do overtly political material, it's a showstopper. His long, complicated and (for the Pub Landlord) surprisingly well informed set piece about 75 million Turks “coming over here, taking our jobs”, which winds itself back to pre-Romans to show what a wonderfully diverse nation we are, and performed in front of a huge, knowingly fascistic backdrop, neatly exposes the toxic notion of British “ethnic purity”.

The routine, reminiscent of Stewart Lee's Ukippers going back to the Big Bang in its reductio ad absurdum quality, is a tour-de-force of comic writing and performance, and worth the admission price alone. But would there were more of it.

• Al Murray is touring until 22 May 2017
• Read more comedy reviews on theartsdesk