By Carla Mozee, MarketWatch

U.K. stocks dropped Thursday, with investors taking a hands-off approach as Britons head to the polls to vote in what's been called the tightest general election in generations.

The FTSE 100 fell 0.8% to 6,877.28, with only 12 shares moving higher. Among those, BT Group PLC and Aviva PLC advanced following financial updates.

The mid-cap FTSE 250 , whose constituents tend to have greater exposure to the U.K. economy, pulled back 0.5% to 17,332.13.

The pound (GBPUSD) was trading at $1.5205 versus $1.5247 late Wednesday in New York.

Opinion polls point to the likelihood that the election will result in a hung parliament, where no party has a majority. The main political parties, the Conservative Party and the Labour Party, will likely have to negotiate with smaller parties to either form a coalition government or reach an agreement for a minority government. Under a minority government, one party would lead, but find support on an issue-by-issue basis from another party. Read: 7 things you need to know about the U.K. election (http://www.marketwatch.com/story/7-things-you-need-to-know-about-the-uk-election-2015-05-06)

"Watch out for the volatility," on the pound, said Richard Perry, market analyst at Hantec Markets, in at note. "Cable is a tough call in the next two days with so many fundamental drivers," including Friday's U.S. jobs report for April.

The first indications of the election outcome won't emerge until after polls close at 10 p.m. London time, or 5 p.m. Eastern Time.

Back to stocks, BT shares rose 0.5% after the telecommunications group's fiscal fourth quarter net profit beat expectations on cost-cutting efforts and a boost from its sports TV channels (http://www.marketwatch.com/story/bt-profit-lifted-by-cost-cuts-sports-channels-2015-05-07-24852536).

Aviva shares picked up 0.6% as the insurer posted a 14% rise in first-quarter new business (http://www.marketwatch.com/story/aviva-new-business-up-14-turnaround-on-track-2015-05-07), and said its turnaround efforts are ahead of schedule.

But Wm Morrison Supermarkets PLC fell 1.9% following the company's report of a drop in first-quarter sales (http://www.marketwatch.com/story/morrisons-q1-sales-down-on-restructuring-costs-2015-05-07).

Subscribe to WSJ: http://online.wsj.com?mod=djnwires