You asked

I would like to obtain the following in regard to the Isles of Scilly:

Population totals for: 1900, 1950, 1990, 2015.

Houses (dwellings) totals for: 1900, 1950, 1990, 2015.

Registered Business totals for: 1900, 1950, 1990, 2015.

We said

Isles of Scilly Population:

1901 - 2,092
1951 - 2,194
1990 - 2,006
2015 - 2,324

Figures for 1901 and 1951 are provided from the relevant census for each year.

Isles of Scilly Houses (dwellings):

1901 - 447
1951 - 541
1991 - 1,169
2011 - 1,388

Please note, the concept of houses/dwellings has been somewhat changeable over the years. The figures are provided from the relevant census for each year.

Isles of Scilly Registered business:

The UK Business: Activity, size and location publication records the number of businesses registered for VAT and/or PAYE broken down to local authority/district level. The number of businesses registered for VAT and/or PAYE in the Isles of Scilly in 2015 was 205 (data are rounded.) Please note these figures do not include very small businesses typically those that fall below the VAT and PAYE thresholds. In 1990 the data were published on a different basis and rather than the number of enterprises (businesses) the publication recorded the number of VAT legal units. In addition to this the Isles of Scilly were included with Cornwall in the publication. Therefore, we have no comparable data for 1990 and unfortunately no data for 1900 and 1950.

https://www.ons.gov.uk/businessindustryandtrade/business/activitysizeandlocation/bulletins/ukbusinessactivitysizeandlocation/previousReleases