My name is derek and I have a ride on mower the engine is a briggs and stratton and there is a knocking noise coming from the sump. Can anyone tell me what this is likely to be and what needs to be done to repair it. Many thanks in avance of any advoice. All the best for now.

It may be connecting rod knock, due to not changing the oil frequently enough. I would tear the engine apart and check things out, paying particular attention to the connecting rod and crankshaft. There's not a whole lot to breaking down these engines. In the future, use the proper viscosity of full-synthetic engine oil. It will virtually eliminate engine-related problems.

Here's an old thread. There seems to be a common problem with these.
https://www.askmehelpdesk.com/tools-power-equipment/briggs-stratton-engine-104357.html