FTSE 100 Index is a market-capitalisation weighted index of UK-listed blue chip companies.

http://www.shareshop.hsbc.co.uk/shareshop/security.cgi?csi=50058

It is made up of these sectors:

Oil & Gas 3 Companies who total market capitalisation is £261,815 Million 13.71% of the FTSE-100
Chemicals 2 Companies who total market capitalisation is £10,113 Million 0.53% of the FTSE-100
Basic Resources 8 Companies who total market capitalisation is £154,949 Million 8.12% of the FTSE-100
Construction & Materials 1 Company who total market capitalisation is £22,673 Million 1.19% of the FTSE-100
Industrial Goods & Services 15 Companies who total market capitalisation is £128,229 Million 6.72% of the FTSE-100
Automobiles & Parts 1 Company who total market capitalisation is £5,467 Million 0.29% of the FTSE-100
Food & Beverage 3 Companies who total market capitalisation is £80,680 Million 4.23% of the FTSE-100
Personal & Household Goods 8 Companies who total market capitalisation is £269,391 Million 14.11% of the FTSE-100
Health Care 6 Companies who total market capitalisation is £184,553 Million 9.67% of the FTSE-100
Retail 6 Companies who total market capitalisation is £41,454 Million 2.17% of the FTSE-100
Media 6 Companies who total market capitalisation is £61,907 Million 3.24% of the FTSE-100
Travel & Leisure 9 Companies who total market capitalisation is £77,673 Million 4.07% of the FTSE-100
Telecommunications 2 Companies who total market capitalisation is £83,413 Million 4.37% of the FTSE-100
Utilities 5 Companies who total market capitalisation is £70,410 Million 3.69% of the FTSE-100
Banks 5 Companies who total market capitalisation is £257,187 Million 13.47% of the FTSE-100
Insurance 8 Companies who total market capitalisation is £115,197 Million 6.03% of the FTSE-100
Real Estate 4 Companies who total market capitalisation is £23,751 Million 1.24% of the FTSE-100
Financial Services 7 Companies who total market capitalisation is £47,625 Million 2.49% of the FTSE-100
Technology 2 Companies who total market capitalisation is £12,521 Million 0.66% of the FTSE-100

Totals 101 Companies, total vaue £1,909,009 Million 100.00% of the FTSE 100 Index.

That is £1.9 Trillion.