Hi Fatiha,
You should account for the wholly attributable (exempt and taxable) input tax in the normal way.
If you are not making taxable supplies in a quarter and are operating the PE standard method then that will potentially skew the Partial Exemption recovery rate.
Taxable supplies over total supplies when both figures are zero will give a zero recovery rate for your residual which would only be resolved at the end of year annual adjustment.
However, if you look at section 4.5 of the PE VAT Notice (706):
https://www.gov.uk/guidance/partial-exemption-vat-notice-706#section4
which states:
For VAT Returns for periods beginning on or after 1 April 2009, you can use your previous year’s recovery percentage to determine your provisional recovery of residual input tax in each period. This is then finalised by way of an annual adjustment. The finalised annual recovery percentage is then used as the provisional recovery percentage for the next year and so on, saving the need to calculate separate recovery percentages for each period.
Therefore, you should be provisionally use the previous years recovery percentage and apply that to the four quarters for this year. Then at the end of the year you should undertake a longer period (annual) adjustment and then account for any difference between the two.
Thank you.