Like 'rector' I was asked to read at the English Mass which, being an Elder in the church in the UK, was very moving.
I once asked a Spanish priest if I, as an Anglican, might take Holy Communion in his Catholic church. He turned to me with his two fore-fingers held togather, and said "Anglican, Roman Catholic - mismo [the same]!" and welcomed me for the next seven years to his services.
Generally, the Catholic church in Spain is very friendly towards Anglicans: remember, they never had the 'reformation'. The same, sadly, cannot always be said of the churches in the UK.
So, rest assured, you will be welcomed at a Communion service in the Cathedral.
Very often, anyone - of any denomination - is also welcome to walk up to the altar rail, keeping their hands in their laps, and maybe head bowed, receive a blessing rather than Communion.
Blessings on every peregrino.
Buen camino!