As you can see from the links below, condensation in cold storage rooms is a common complaint and is related to high humidity levels and cool concrete surfaces. Since the problem has developed in the last two years, you should think back to any house or household changes that took place around that time, even if they don't seem to be related. The house operates as a system, so a change in one area can cause an effect in another, apparently unrelated area. The most likely change is one that increased the humidity of the home, since there are few changes that would change the temperature of the concrete. Some possiblecauses to consider might be:
Was an old fuel-fired boiler replaced with the current electric boiler two years ago? Fuel-fired boilers use a chimney, which creates a significant amount of ventilation in the home. Abandoning this will reduce ventilation rates and slow the exhaust of humidity.
Did you start storing wood inside the home then? Drying wood can generate a lot of moisture.
Are there more people, pets, or plants in the home? All of these contribute to the moisture load. Even if the number of people doesn't change, children who grow into often-showering teenagers can cause humidity levels to rise.
Were there changes to exterior landscaping or to downspout drainage? If water is not draining well away from the home, it can saturate the soil and wick into the basement, increasing the humidity.
Were the windows updated? Newer windows are much less leaky and drafty. This means that there isn't as much natural ventilation available to remove excess moisture from the air.
There are any number of other possibilities, but try to think of things that changed around that time and see of they can be addressed. Often, the solution is to add more mechanical ventilation to the home, or to more regularly use the ventilation that already exists.