Urgent help needed e36 M3

Hi guys, having a spot of engine trouble. Started the car earlier to go to work, drove off fine and after about 200 yards the engine started to plutter. Fells like its down a cylinder. Drove home slowly and had to leave it. I'm hoping its a spark plug but what else should I check? Also what spark plugs should I buy and do Halfords sell them as they're the only place open today.

Thanks, Alex.

Thanks, I've had a look under the bonnet with a friend but can't see anything too obvious.

Here's what happened. Bought the car Wednesday night. It was very very low on petrol so I filled it up. Car ran perfect for 200 miles. Yesterday I did have a go at cleaning the engine. I sprayed Gunk on some parts and rinsed with water. The engine was hot and it ran perfect on a 10 mile journey afterwards. Then later, I was stuck in a VERY bad traffic jam because of an accident. It was bumper to bumber for about an hour. When it cleared the car was running fine. As I was driving up the hill towards my house I did notice a slight hesitation but I didn't think anything of it. Left the car overnight. Today at about 1pm I started it and drove out of my gate and down the hill. Car sounded perfect, then going up the next bit of a hill it lost power and started shaking and spluttering so I turned and went home.