Doi I need to take any immediate action or just cotinue to monitor the moisure levels?

In most cases, above 22%WME is considered the beginning of damp. Secondly , a damp meter cannot be used on a building older than 100 years because they set off damp meters when no dampness is present . Visual damp damage is the only way to monitor the property .

Moisture readings are always higher around both windows and doors, especially in a solid brick wall house. This is known as thermal bridging. Modern houses are constructed to prevent this. If you have no issues, such visible damp or mould, you could certainly do nothing, there is no reason for it to get worse. Make sure you have window ventilation, trickle vents are best. You could paint the external brick around the windows with a clear water repellent, this is invisible and considerably reduces the amount of rain soaking into brick and will reduce the moisture soaking in to the inside around apertures. Otherwise, I can see no reason to do anything else. Hope this helps.

In my opinion readings of 25/30% would need treatment, it's also good practice to maybe look into prevention treatments on the lower reading areas in the vicinity.

Not really sure why 3 people on here have failed to mention the obvious. If you are trying to ascertain the moisture content of a wall then you need to test inside the wall. A damp meter probed only on the surface is 100% irrelevant. It simply proves you have condensation until you take a sample that confirms it, or otherwise. Throw that damp meter in the bin its 100% useless. Drill into the wall. Wet? Or dry? If you think your car engine is broken... Open the bonnet and check. Those silly plastic damp meters are the reason people waste thousands of pounds on often uneccasary treatments.