We finally found some Seville oranges, although we had to go on the web to find a local shop who stocked them just 6 miles away.     Ironically, the following day we did find them in Waitrose.

The best method I found for making the marmalade, was to boil the fruit whole the previous day, much less arm aching juicing this way.  

Covered the fruit with water and simmered for 3 hours (12 oranges and 2 lemons), with a tight fitting lid, or if you don't have a large lid you can use double foil, so you don't loose any from evaporation.   Do check to make sure that it hasn't boiled dry.

Next day remove the fruit.   Don't discard the poaching juice this is required for the marmalade.

Cut fruit in half and scoop out the flesh into another pan. 
Bring the flesh and pips to the Boil and then simer for half and hour.   Pust a sieve, lined with muslin' over the pan containing the poaching liquid. The tie the muslin bundle to the handle of the preserving pan to drip into the poaching juice.

Meanwhile, discard the lemon skins and slice the orange skins up by cutting in half again (now in quarters) and then into shred slices.  Make a chunky or thin as you like it.   Keep these on a separate dish for the moment and pour any remaining juice into the poaching liquid.

Squeeze the muslin bag into the poaching liquid, by putting two wooden spoon handles together through the knotted muslin and twisting in opposite directions until you have got nearly all the juice out.    Discard pulp.

Measure the liquid, you should have 4 pints at this point.   If not then add water to make up to that amount.

Put at least 6/7 jars in the oven on Gas  mark 1 or 140 C to warm, upside down or on their sides.
Put the lids, and funnel and ladel in a pan to boil for at least 10 mins in some boiling water to sterilize.

Now add the peel to the 4 pints of juice and bring to the boil, then add 4lb of warm sugar.   I used a mix of pectin added granulated and ordinary granulated sugar.    Stir constantly until the sugar has disolved and then boil for 15 mins.

After this time test a small amount on a plate which has been in the freezer for at least two minutes.   Return plate to the freezer for two minutes and push finger along liquid, if a rippled skin forms then the marmalade is ready to bottle. (if you're not sure it's got a skin, keep going, it will be obvious).
It took me 55 mins to get to this stage, but it is wise to test every 5 mins, especially if you use all pectin added sugar.   I left my pan on the stove still bubbling whilst waiting for the plate to come out of the freezer, but when it got close to nearly being set I tested ever 2 mins.

NOTE: the marmalade or jam will have lots of tiny bubbles before it reaches this stage, and they get bigger and more gloopy the nearer to setting it gets.

If you are still not sure it's set, then cover the pan and leave until the next day in the pan.   If not set then bring to the boil for a further 3 mins and leave again to the next day.    I did this with some Quince Jam over a period of 4 days and it was perfect.    The reason for doing Quince this way, is that it intesifies the colour.