There are some basic documents required for all visa applicants apart from the specific categories. Following are the necessary documents required for a Schengen visa application process-

• Applicant must have valid and signed passport which should not be older than 10 years with 2 blank pages. Also make sure it remains valid for 3 months beyond the trip.
• A recent passport sized photograph is required with white background. Make sure the photograph should not be older than 6 months. All facial characteristics should be clearly visible on a non-damaged passport sized photograph.
• UK Residents Permit is required to apply visa from UK. BRP could either be stamped in the passport or in the form of Biometric card.
• Hardcopy of original visa application form filled with correct details using pen.
• Travel insurance is required which is common for all Schengen countries for period of one year. The valid travel insurance should cover the medical expense of at least €30000.
• Proof of travelling is required including round trip flight tickets, and stay in the country. Letter of invitation is required if you’re staying at your friends or relatives. 
• Proof of sufficient fund is required as per your stay period in Portugal. Bank account should hold at least €90 for each day of stay.
• Cover letter specifying the details of your trip is required to submit. 

Come to additional documents required for employed/self-employed/ or retired category applicant for Portugal visa UK.

Specific documents required for Portugal visa-

If Employed-

• Letter of Employment
• 3 months latest bank statement
• Last 3 months of pay slips

If Self-employed-

• Copy of business license
• Proof of the company
• 3 months bank statement

If Retired-

• Proof of retirement letter
• Pension slip for last 3 months