Quedos

Stig -
the stat minimum notice perios any employee needs to give his employer is one week. HOWEVER the contract will state in fuller terms the expected notice the employee shall give.

Only if the contract is silent will the Stat Min Notice Period take precedent if you have worked one month or more (the caveat as always A much longer notice period may however be implied if it is reasonable in all the circumstances (i.e. what is normal for a person of that seniority and in the industry such as MD's and Directors)

So you are right to state that your notice is 4 weeks as this is stated in your contract

Evidence employment law notes from Unite trainig course