I did a quick experiment to find out which was more efficient for making a mug of tea: the kettle or the microwave.
Kettle: 3 KW
Microwave: 700 W
The kettle took almost exactly 1 minute to boil a mug of water.
The microwave took about 3 minutes.
Energy used / Kettle = 3,000 Watts x 1/60H= 50 WH
Energy used / Microwave = 700 Watts x 3/60H = 35 WH
A saving of 15 watt-hours per mug. I probably have about 8 mugs of tea or coffee per day, so a saving of 43.8 KWH / £6.25 per year on my current tariff.