The US census scheduled for next year may not be able to count gay married couples due to technical issues in collecting data.

US Census Bureau officials said in June that the 2010 census will count married gay couples, despite previous statements that they would not be recognised.

The last census was carried out in 2000, when gay couples could not marry in any state. Now, six states allow gay marriage and those who married in California before Proposition 8 are still legally wed.

However, USA Today reports that a host of issues may prevent the marriages of gay couples from being recorded.

Currently, the software used automatically converts same-sex married couples to unmarried partners, something that the bureau is unsure can be changed before 2010.

Another issue is that although the federal marriage act does not apply to the Census, it does apply to every other federal agency that uses Census data to calculate federal funds and enforce equality and housing laws.

Finally, data used by all federal agencies such as income and family size would have to be reclassified as including same-sex married couples as families would have a domino effect on other data.

Previously, the federal Defence of Marriage Act, signed in 1996 by President Bill Clinton, barred the information from being collected. However, the White House announced in June that its interpretation of the act did not prohibit gathering the information.

White House press secretary Robert Gibbs said: “The president and the administration are committed to a fair and accurate count of all Americans.

“We’re in the midst of determining the best way to ensure that gay and lesbian couples are accurately counted.”

The next UK national census will be held on 27th March 2011. For the first time the marital status question will include a civil partnership option, but there will not be a question on sexual orientation.