Thanks both, makes sense too me 1:1 thought I might be missing something as the FERA Bee unit guidelines say 2:1 with foundation. Copied and pasted instructions. Maybe I should ask them why they recommend 2:1 with foundation!
As Per their guidelines;
Prepare a clean brood chamber filled with frames of foundation. Place this chamber over the existing brood chamber. Unless there is a strong nectar flow feed with winter strength sugar syrup i.e.1/2 litre of water to 1 kilogram of sugar. When the bees have drawn out some of the foundation, find the queen and place her on this comb. Put a queen excluder over the old brood chamber and under the new, thus trapping the queen in the upper chamber. If possible arrange a new hive entrance between the two brood boxes and close off the old. (This helps to reduce the amount of pollen stored in the old lower combs. After three weeks remove the old brood chamber. The brood will have hatched and the comb can then be rendered to recover the beeswax.
This system is ideal for replacing all the combs at once and is best performed in early spring often, with clement weather, March is suitable, but remember to keep feeding so the bees can build comb.