Carbon, cold starts and plugs that never burn clean
A spark plug runs best when the engine is hot and under load, because that is when deposits burn off the electrode and the insulator. Morden driving offers very little of either. Central Road and the town centre around the station are dominated by buses, stands and crossings, trips from Morden Park or the streets near Morden Park House are short, and the engine often spends the whole journey below the temperature at which anything burns clean.
The result over two years is a plug with a carbon-coated insulator nose, a worn electrode and a wider gap than it left the factory with. The coil compensates by generating a higher voltage until it cannot, and the symptoms arrive in a familiar order: longer cranking on a cold morning, a slight stumble pulling away, then a misfire under load. Each of those is cheap to prevent and progressively more expensive to ignore, because a misfire damages the catalytic converter.
At a major service we fit plugs of the exact type, heat range and gap your engine is specified for, from NGK, Denso or Bosch, torqued to specification rather than nipped up by feel, with the coil boots inspected and greased where appropriate. If your engine is a diesel the equivalent item is the fuel filter, where it has a serviceable one. Brake fluid is changed completely, from a sealed container, moisture tested before and after.
Everything in the full service comes with it: oil and oil filter, air filter, cabin filter, the wheels-off inspection with brake measurements recorded, coolant and battery tests and a fault code scan. Allow most of the day. The drive is Morden Hall Road to the roundabout, Morden Road past the park into Mitcham, then Cranmer Road and Carshalton Road, about twelve minutes, and collection and delivery can be arranged.

