what happens if you do not work your four weeks notice with employer

[emandjules]

with civil service anyone know...

I assume you mean that you hand in your notice but leave straight away instead of working your notice?

In theory, you can be sued for breach of contract. However, an employer has to have financial losses as a result of the breach for this to be worthwhile. Normally, they don't.

In reality, nothing happens. You just won't get paid for the bit you don't work.

It can affect a reference in the future.

I left a job with 7 days notice despite needing to give a month. They threatened to sue me, but I maintained my stance continued to work hard for the week, apologised and left.

In the end, they admitted they wouldn't have really taken me to court as not financially viable and made the threat so I would stay.

Keep your head down, do not rock the boat, maintain your stance and hopefully they will accept your decision with good grace.

They won't pay you for the last four weeks, I would guess. Or if they do, they might try and claim it back.