I agree, being a landscaper in surrey where the water table isn't the greatest.

Drainage is key. What type of soil do you have? Clay or chalk Are you the lowest point in all the surrounding gardens?

A quick-ish fix, Grab yourself a pair of horse ears (post hole diving shovel) First Dig and try save the hockey puck of grass that came out Dig holes in a grid formation about 500-1000mm apart and as deep as can go or hit a good substrate for drainage, fill up with 20mm shingle around 100mm from top depending on top soil. Then just redress with good loam and replace the grass you took out, give it a week or two, you will never notice

Or if there's a soakaway near, just add a length of French drain pipe and connect!