REVEALED: The 50 seats where an 'Anti-Reform Alliance' is plotting to block Nigel Farage's path to No10

Reform UK's support soared from just 495 votes in 2021 to 12,113 in this week's by-election.

Meanwhile, Plaid Cymru's vote total jumped from 8,211 to 15,961, hoovering up a huge drop in support for Labour and the Liberal Democrats.

Despite being buoyed nationally following Zack Polanski's leadership victory, the Green Party failed to retain its deposit after securing just 516 votes.

Plaid Cymru's claim to be the main challenger to Reform UK was emboldened last night, prompting speculation that the two insurgent parties could soon be vying for top spot in Wales.

However, polling guru James Johnson told GB News that other parties will also look to rally support on an anti-Reform UK ticket, including the Liberal Democrats and the Labour Party.

So, where could Reform UK miss out when up against a progressive alliance?

Aberafan Maesteg, Aberdeenshire North & Moray, Ayr, Carrick & Cumnock, Barking, Basingstoke, Blackley & Middleton South, Bury South, Bournemouth East, Caerphilly, Cardiff East, Canterbury, City of Durham, Colchester, Croydon East, Coventry East, Dumfries & Galloway, East Worthing & Shoreham, Eltham & Chislehurst, Feltham & Heston, Filton & Bradley Stoke, Gedling, Gower, Hamble Valley, Hastings & Rye, High Peak, Hitchin, Ipswich, Lancaster & Wyre, Milton Keynes Central, Milton Keynes North, Newcastle upon Tyne East & Wallsend, North Cotswolds, and North East Somerset & Hanham could all be kept out of Reform UK's hands.

The same situation is possible in Norwich North, Nottingham South, Plymouth Sutton & Devonport, Runcorn & Helsby, Shrewsbury, Smethwick, South Shropshire, St Helens South & Whiston, South West Hertfordshire, Truro & Falmouth, Warrington South, Watford, Welwyn Hatfield, West Lancashire, Wolverhampton West, Wycombe, and Swansea West.

Despite Reform UK consistently leading in the opinion polls, Mr Farage remains behind his main rivals in head-to-head contests.

Sir Keir Starmer, whose personal favourability is lower than compared to Mr Farage, is seven points ahead of the Reform UK leader.

Meanwhile, Liberal Democrat leader Sir Ed Davey was four per cent of Mr Farage in YouGov's August tracker.

Mr Farage only performed better than Tory leader Kemi Badenoch, albeit by a meagre two per cent.

With most contests across the country coming down to Reform UK versus Labour at this moment in time, Sir Keir also has a net lead of 51 per cent among 2024 Green Party voters and 38 per cent among 2024 Liberal Democrat supporters.

Sir Keir's collapse in support might complicate matters but there is evidence of more tactical voting in British politics.

One-in-five voters admitted they had decided to vote tactically in the 2024 General Election, including 29 per cent of Labour voters and 39 per cent of Liberal Democrat supporters.

More recent research conducted by Electoral Calculus suggests over a third of Labour voters would even vote Conservative to keep Reform UK out.

Electoral Calculus found that tactical voting could cost Reform UK 67 seats, resulting in Labour picking up an extra 42 and the Tories securing an additional 29 seats.

The company found that 54 per cent of Tory voters would back Reform UK in Labour-Reform battleground in Wales, with 48 per cent of Plaid Cymru supporters lending their vote to Labour.

Meanwhile, Reform-Plaid battlegrounds, including Caerphilly, witnessed 46 per cent of Tories break for Reform and 65 per cent of Labour voters side with Plaid Cymru.

Here's an example: Gower

The Gower was a Labour seat from 1909 to 2015, falling into David Cameron's hands before being snatched back in 2017.

Tonia Antoniazzi retained the seaside seat in 2024, opening up an 11,567-vote majority over the Tories.

However, Election Maps now has Reform UK on 30.2 per cent, 6.7 per cent ahead of Labour on 23.4 per cent.

If Electoral Calculus's findings are mapped onto the seat, Labour's support could jump to 30.8 per cent.

Meanwhile, Reform UK could jump to 36.1 per cent if Tory switchers follow Electoral Calculus's model.

But Reform's 5.3 per cent advantage remains vulnerable given 7.8 per cent of Gower voters would currently support a Liberal Democrat candidate and 10.5 per cent would opt to vote for the Green Party.