Two sites, only one listing

[stampman]

We have two sites.

1) http://www.stampsdirect.co.uk

2) http://www.rubber-stamps.co.uk

Site 1 is positioned on page one of Google when searching for rubber stamps within the UK.

Site 2 doesn't appear.

Both sites have similar content.

We only want one site (No. 2), but obv don't want to lose our high ranking.

Why isn't site 2 being ranked as high as site 1.

Is it because they have similar content?