The FT 30 (FT Ordinary Index or FTOI, not "FTSE 30") is a now rarely used index that is similar to the Dow Jones Industrial Average. It has since been superseded by the FTSE 100, introduced in 1984.
The companies listed in the index are made up of those in the Industrial and Commercial sectors and exclude financial sector (banks, insurance, etc.) and government stocks.
References
Oxford dictionary of Finance and Banking, ISBN 0-19-860749-0
Berger, D. & Jackson, B. ; The Motley Fool UK investment workbook, ISBN 0-7522-1787-9