Should I be using 'P' scales to record the progress of early stage EAL learners?

No. The P scales must not be used to assess children with EAL at any age, unless they have additional special educational needs. The SEN Code of Practice is quite clear that:

A child or young person does not have a learning difficulty or disability solely because the language (or form of language) in which he or she is or will be taught is different from a language (or form of language) which is or has been spoken at home.

Teachers are expected to use the National Curriculum English attainment levels for the statutory assessment of the English language development of pupils with EAL. However many schools use different assessment methods and materials, including EAL stages to record bilingual learners progress. .