Obviously a complete renewal of the cable would be a better option! But if this will involve lots of upheaval bet yoursel the appropriate sized connector usually 5 amp rated,to connect the two severed ends together (thats if they still reach) choclate block or straight through crimp (blue in colour for 2.5mm) can be utilised and then ensure you cover this with insulation tape. Always remember to isolate the circuit to be worked on before any work is carried out.
Charlie
February 2009