ELI5 What causes these irregular tides?

On holiday in Wells-next-the-Sea in Norfolk, UK, and according to the Met Office the tide times today are

First Low Tide: 03:28 at -0.6 metres

First High Tide: 07:37 at 3.3 metres

Second Low Tide: 16:07 at -0.8 metres

Second High Tide: 20:23 at 3.3 metres

I'm used to tide timings being fairly regular - how come these are ≈4hrs low to high but ≈8.5hrs high to low?