The South Wales Valleys: Wales' big EU battleground
The main battleground in Wales in the final week of the referendum campaign will be the south Wales valleys.
This will be ripe territory for both sides because they believe that is where the highest numbers of undecided voters are to be found.
Morgan Brobyn, from Vote Leave, said he was looking to take advantage of the split loyalties many feel because of their previous support for remain-supporting Labour.
He said: "It is a combination of failed aspirations which they see around them and because they don't see any tangible benefit to the EU or any difference it's made to their lives.
"The level of structural funding is not enough of an incentive for them to remain."
Lord Hain, who is running the Welsh Labour In campaign, said between a fifth and a third of voters in its heartland areas were undecided.
He said: "People are beginning to get alarmed. We are going to have to fight for a vote that people took for granted.
"There is a big section that is undecided and they will hold the key."
It means that rock-solid Labour areas will become political battlegrounds during the next week, in marked contrast to normal elections where the results are often foregone conclusions.
Unlike in a first-past-the-post general election, every vote in a referendum counts as the the entire UK. In effect, becomes one giant constituency.
The Valleys feature prominently in the areas that Vote Leave will be focusing on in the final days of the campaign.
As well as Merthyr Tydfil and Caerphilly, they include Port Talbot, Cardiff and Newport.
In the north, extra resources will be deployed in the constituencies of Clwyd West, Aberconwy and Wrexham.
Leave campaigners say their blanket leafleting approach will be replaced by more targeted door-to-door canvassing in the final days.
Any undecided voters expressing some degree of sympathy for a Brexit to a Vote Leave campaigner can expect another visit on June 23rd as the campaign focuses on getting its vote out.
Senior Vote Leave figures admit some of their data is too narrow but they believe they are ahead in most parts of Wales apart from Anglesey, Gwynedd, Ceredigion, Cardiff and in Newport where they say they are neck-and-neck with remain.
They claim to have had up to 500 activists operating in Wales in the past week.
The make-up of the teams vary. In the Vale of Glamorgan, around 80% of the local Conservative activists who campaigned for the party in the recent assembly and general elections are out campaigning for leave.
The remain side is more difficult to characterise because it is made up of a number of different elements.
Wales Stronger In is the umbrella organisation, but it works alongside parties like Plaid Cymru, and parallel with the much larger ground operation run by Labour.
Labour has run a separate operation involving up to 1,000 people on a weekly basis, and has focused entirely on traditional voters using a combination of doorstep canvassing and town centre stalls.
From here until the referendum, Labour's focus will be in the south Wales valleys and Newport, where the party admits there is plenty of heavy lifting to be done.
Lord Hain believes in some areas it is developing into a head versus heart debate.
He says people have begun approaching them saying their heart wants them to leave but their head is telling them to stay.
And it is this remark which they are latching onto, as the leave side try to generate a sense of momentum in the final stage of the campaign.