History of the British peerage

The history of the British peerage, a system of nobility found in the United Kingdom, stretches over the last thousand years. The origins of the British peerage are obscure but while the ranks of baron and earl perhaps predate the British peerage itself, the ranks of duke and marquess were introduced to England in the 14th century. The rank of viscount came later, in the mid-15th century. Peers were summoned to Parliament, forming the House of Lords.

The unions of England and Scotland to form Great Britain in 1707, and of Great Britain and Ireland to form the United Kingdom in 1801, led successively to the establishment of the Peerages of Great Britain and later of the United Kingdom, and the discontinuation of creations in the Peerages of England and Scotland. Scottish and Irish peers did not have an automatic right to sit in the House of Lords, and instead elected representative peers from amongst their number.

Peerages were largely hereditary until the regular creation of life peers began in the second half of the 20th century. The last creation of a non-royal hereditary peer occurred in 1984; even then it was considered unusual. Life peers and 92 hereditary peers still retain the right to sit and vote in the House of Lords, though their power is restricted and further reform of the House of Lords is under consideration.

...
Wikipedia