>>>How do I know if it is registered at the land registry or are all properties registered there
If it's changed ownership since 1990, then 'yes'. If it hasn't, then 'possibly':
http://www.landregistry.gov.uk/public/faqs/is-all-land-registered
Title registers to land (including the properties thereon) are publicly available for a fee of £3. If you enter your house number (or name), together with your postcode, here and you're offered the opportunity to buy the title register (and title plan) then your property is definitely on the register:
http://www.landregistry.gov.uk/public/property-ownership
(You don't have to buy them!)