Plans by British prime minister David Cameron to move the clock forward in Northern Ireland could have a significant impact on business practices here if the Republic does not follow suit, according to one Dublin- based solicitor's firm which provides services to clients in both Spain and Portugal.

David McDonnell, a partner in McGrath McDonnell and Associates, said that since both countries are on different time zones – Spain is one hour ahead of Ireland while Portuguese time is the same as here – his working day would typically begin at 8am in order to catch the Spanish banks and other businesses as soon as they open.

"If you are getting into the office here at 9am, it is already 10am in Spain," he said. "Usually when you are closing a [property] deal, you need to make the most of all the hours that are available. It can have huge ramifications for your client if you miss deadlines.

"If you need to speak to someone, that can be a problem too, for example if they have left the office because you are working on Irish time and don't factor in the extra hour."

Cameron recently signalled that he may back the proposal to change Greenwich Mean Time, the UK's time zone, and stressed that if he did it would be implemented across the UK.

This would mean a town in Northern Ireland such as Newry would move into a different time zone to Dundalk overnight.

But if the Republic moves time zones as well, the sun would not go down on Galway Bay until close to 11.30pm at the height of summer, while at the winter solstice, it would not rise until at least 9.40am.

McDonnell said the hour difference in time zones between Spain and Portugal is a factor throughout the year, although it is compounded by the fact that opening times and general working hours in Spain are significantly curtailed during the hot summer months.

By comparison, because Portugal is in the same time zone as Ireland, there is far less of an impact on the working day. However, it also means his office works right through to closing time there, even though the Spanish side of the business would have been long closed for the day.