Here’s how Constance Marten and Mark Gordon are evading detection

I have spent decades tracking down wanted people – even those who had evaded the police for years

Runaway heiress Constance Marten and her partner, Mark Gordon, have been at the centre of a nationwide police hunt for the last two weeks. We don’t yet know why Marten and Gordon have chosen to go on the run – or how long they’ll manage to evade detection. But after decades of experience in tracking down wanted people, I can tell you some of the ways I believe they have managed to go “off-grid”.

As each day goes by, we are learning more and more about their lives. We know they are wanted not only because of concerns for the welfare of their newborn son, but because of Constance herself – who may not have been seen by medical professionals since his birth.

Such haste to get from the north to the south of England suggests they had already identified a place to lie low and hide. But how are they both managing to stay hidden? Here are some key ways:

• Not using credit cards because they can be tracked to location of use.

• Using false names allows them not to be instantly recognised. I highly suspect that they will have already set up aliases, which will have their own “legend” or backstory giving some level of authenticity.

• Cash is king when you are on the run. It is untraceable, but they will have planned out carefully how much of a stash to take out and how long it will last. We know they have “substantial” cash allowing them to live “off-grid” – but at some stage it will run out, causing them to resurface to withdraw more. What is “saving” them at the moment could therefore become their downfall.

• Mobile phones are now key to tracking people and this is why I am sure they will be using burner phones. Authorities have tightened up on the sale of both the handsets and sim cards, requiring names and address to be given. But you can easily get your hands on a false one, or go to a back street seller. Key for Marten and Gordon will be that nobody finds any number they have or the phones themselves – as they may well then hold useful location data.

• They will be using Airbnbs, with key search words – “entire place” and “lockbox” – so as to keep contact with people to an absolute minimum.

• Winter is much better for hiding in plain sight – they will be wearing plain-coloured clothing so they don’t stand out, and loose clothing which can totally change your body shape. Hats can hide full facial features, too. Interestingly, very few people who go on the run change their identity very much – they may dye their hair or remove (or grow) facial hair, but they likely won’t do anything too substantial.

• The simple key to staying hiding is isolation. They will have found a safe and secure location, where they can’t be tracked to – and will have cut contact with outside world. But they are also making mistakes, such as using taxis and public transport. These mistakes will increase over time, especially with the growing media and public interest.

• They have lived for years cut off from existing friends and family, so unlike most people on the run, they will probably not reach out to them for help at this stage – but they will eventually.

Everything tells me that they are still in the UK, having missed the opportunity to leave the country in the very early days. If they were going to leave, they would have done so right away. And we know they haven’t.

I have spent decades tracking down wanted people. In my ITV series, On The Run, I tracked down those that had evaded the police for years – and as head of social operation on Channel 4’s Hunted (a real-life thriller where ordinary people go on the run from a team of expert hunters) it was being one step ahead of former military intelligence officer Mervyn that enabled me to catch him. I knew he had little money, so needed to use public transport – and so I plotted all his possible routes from the last location he was positively identified at.

When people don’t know an area, they tend to head for bigger cities and towns, which offer less familiarity that a small village. A stranger in a small village will be noticed. So, when I was tracking Mervyn, I plotted the units with view of the main bus station and also one stop before.

Why? Well, because the stop before was still close enough to the centre, but unlikely to have CCTV (unlike the main bus station). Mervyn would have known that. And yes, he got off the bus just before the main station – and we got him.

It is only a matter of time before Marten and Gordon are spotted.

Mark Williams-Thomas is an investigative reporter. He is also the presenter of ITV and Netflix series The Investigator