This description is provided by Olive Thexton of Fylde Branch

ONS - The Office for National Statistics 

This is the Government department that issues copy certificates of births, marriages and deaths since1837.

To order a copy certificate, you need the reference number from an index. The nearest place holding an index you can inspect is likley to be a main refernce library, or the Lancashire Record Office in Preston.

The indexes are for quarters of each year (Mar, Jun, Sept, Dec) then alphabetically by name within that quarter. If you find your ancestor and have noted all the details i.e. name, year, quarter, place, volume and page number, you then have what you need to order a copy of the original certificate from ONS. 

The information on the certificates can give vital information to take you back another generation. In the case of Marriage certificates it is advisable to cross check the bride and grooms names if you have them. 

You should find the same reference number for them both although occasionally they may be in consecutive quarters!