Preheat the oven to fan-assisted 240C / 220C / 425F / gas 7.
Mix together the pesto and anchovies
Stuff the rolled lamb with the pesto mix and roast in the preheated oven for 20 mins.
Then reduce the heat to fan-assisted 140C / 160C / 325F / gas 3 and roast for 10 min per 500g / 1.1lb for rare or 20 mins per 500g / 1.1lb for well done.
Use the thermometer to check your meat.Your reading should be 50C / 122F for rare and 70C / 158F for well done.
Allow the lamb to rest for 20 mins before carving.