If its an apartment,it's definitely leasehold. Its' almost certainly for a term of 500 or 999 years.
I know from personal experience with Pepper that they are not particularly helpful.
You could try asking the solicitor who handled the original conveyancing if they have a Schedule of Deeds? It's bit cheeky if you're doing the Probate yourself.
Otherwise, you could just describe the property as Leasehold, 500 years, with a term commencement date of January 1st whatever date the property was bought, if bought from new, or January 1st from whatever year it looks to have been built. Very little turns on it in the CA24
mf