Can a 'nationalist alliance' threaten the future of Keir Starmer?

Yet afterwards, both men were at pains to say it was tackling child poverty which had been the focus of conversation and is the subject which lies at the heart of the "progressive alliance" they are seeking to forge.

Well if you believe that, I've got a prime retail opportunity in the centre of Edinburgh with its own esplanade and set of cannons to sell you.

While the two men talk centre-left politics, and no doubt believe in eradicating child poverty wholeheartedly, what most binds them and their parties is a desire to shrug off the rest of the UK. This is an alliance cemented by the mortar of the dream of independence.

Not that today was the first time such a nationalist bond was on public display - Nicola Sturgeon and Leanne Wood were always keen to show just how well they got along when both led their parties.

They never got as far as discussing an alliance as such. But while FM Sturgeon was also keen to work with former Welsh FM, Labour's Mark Drakeford, when it came to a joint approach on devolved matters if both felt they were being hard done by especially financially, by the Conservative UK government.

The difference now is that there is an actual possibility that Plaid Cymru will break Labour's hold on Wales next May, and that the SNP will continue to be in power in Scotland.

Speaking to journalists afterwards, it was all a bit "don't scare the horses", from the Plaid leader, who knows that independence isn't high on Welsh people's current political priorities.

While polls show the gap closing between those in favour of indepence and those against, it's the economy and the health service which are uppermost in voters minds and a dissatisfaction with the UK Labour government.

But while ap Iorwerth has been emphatic that independence won't be at the heart of his campaigning for next May, voters in Scotland could tell you how quickly that will change should his party succeed. It's the "lend us your vote even if you don't support independence" strategy used incredibly successfully by the SNP for decades.

Welsh voters will have to decide if they believe it or not.

John Swinney meanwhile has put independence front and centre of his campaign for next year in an attempt to secure a majority of MSPs and he hopes force a second referendum.

So the two parties are operating at different levels on the independence question. Plaid appear to be roughly in the same position the SNP were going into the 2007 elections which secured the nationalists their first term in charge of the Scottish Government - as a minority administration. Let's show you we can govern, and then you'll be convinced on independence was Alex Salmond's line then - and it seems to be one ap Iorwerth believes can work for him.

Swinney's line now is that Labour have changed nothing for the better - so Scots are better off out of the union altogether. It wouldn't be surprising if that's repeated by ap Iorwerth the day after the election should he be Wales' first Plaid FM.

And if both parties do win? Well a UK with two nationalist governments at opposite ends of the country will be a severe headache for a unionist Prime Minister, who may also find that Labour gets hit at the ballot box in the English local elections. It will very likely have huge consequences for Keir Starmer.

John Swinney has been very public in his belief that Labour - and therefore the UK government - would need to find a new leader should that particular nationalist earthquake occur. ap Iorwerth has been less forthcoming in that regard, telling LBC only that it would "put a huge amount of pressure" on Starmer.

Both men scent victory in the air. Yes, there's a long way to go but the Labour vote appears to have collapsed in Wales and has been falling ever since the General Election in Scotland.

Of course there is no certainty that any win by the SNP and Plaid would force a UK government to do anything on the constitution - voter turn outs, percentages, polling on the independence question itself will all come into play if and when any referendums are demanded.

But the result would send shockwaves through Labour. Scotland slipped from Labour's grasp many years ago. Wales could follow suit. If Keir Starmer is at the helm when it happens, he could find the pressure for him to go will be too much to ignore.