This wil all be detailed on your original mortgage offer. Dig out the document and look towards the back, sections 10 & 11 will detial early repayment penalties.
I would imagine anywhere between 3% & 5%, which may well mean it is not worthwhile remortgaging purely to save money.
If you are looking to raise extra finance, you may be able to do so via a further advance with A&L.
If you need more detailed advice regarding the early repayment charges, contact a
mortgage broker who will be able to discuss them with you and also tell you what alternative options are out there.