Can self-raising flour be used in lieu of plain flour when making a roux for a bechamel? I have plenty of self-raising flour (which will easily take me until its best before date to use) but am running very low on plain flour which I use predominantly for making a roux and then ultimately a bechamel. Given the current circumstances it seems appropriate to use up things I already have in the cupboard, rather than purchasing more if I don't need to.

Will the added raising agents in self-raising flour (the flour I have is from Sainsbury's and contains Calcium Phosphate and Sodium Hydrogen Carbonate, apparently) affect the production of a roux and then ultimately a bechamel sauce from the roux?
Since you will only be using 1.5 tablespoon of flour for more than a cup of milk, it shouldn't impact the flavor. Also as there is no salt in the Sainsbury Self-raising flour, you will not need to adjust for salt. However, the alkalinity from the Sodium Hydrogen Carbonate as it heats and breaks down into Sodium Carbonate might impact the flavor. But, the acidity of the milk and butter should counter that, so it wouldn't be noticeable.