Heat oven to 160C/140C fan/gas 3 and put the chicken in a roasting tin.
Put the butter into a small bowl and add the herbs and plenty of seasoning. Grate in the zest from the lemon and mash everything together with the butter using a fork. Rub this over the chicken breasts, legs and wings, then push the whole grated lemon into the big cavity of the chicken.
Pour half the stock into the tin. Use a large sheet of tin foil (or a couple of smaller pieces) to cover the chicken and scrunch together the foil along the edges of the tin so the whole thing is sealed. Put in the oven and set your timer for 2 hrs.
Carefully remove the foil from the chicken, increase oven to 220C/200C fan/ gas 7, and put the chicken back in for another 30 mins. If youre making the Crunchy roast potatoes (see 'Goes well with'), put them in now, under the chicken. After 30 mins, take the chicken out of the oven and lift it onto a serving dish (move the potatoes up). Snugly cover the chicken with foil and set aside while you make the gravy.
Tip the chicken juices and stock from the tin into a jug.
Put the tin over a medium heat on your hob and use a wooden spoon to stir in the flour and Marmite, if using, with a splash of the juices to make a paste. If you want, spoon the fat off the top of the chicken juices in the jug, then gradually stir this into the tin to make a smooth gravy.
Add as much of the rest of the stock as you need to make a good gravy, then serve with the chicken.
