Type 23 Frigates have the CODLAG propulsion arrangements: Combined Diesel Electric and Gas Turbine. Normal cruising - and towed array operations - would be Diesel Electric, with Gas Turbines for sprint power. She therefore has 4x GEC Alsthom Paxman Valenta diesel engines (similar to high speed train engines), 2x GEC electric motors and 2x Rolls Royce Spey (the same type that was fitted into RN Phantoms, ironically) gas turbines. Hence the number of funnel exhausts.
In addition the the range of powerplants available - another reason for the odd/bulky shape of many modern warships are some special masking 'Features' added to the funnel exhausts to help reduce the thermal signature and protect the ship from IR targeting/IR homing missiles.