(BRUSSELS) - Internet service providers in Europe are charging wildly inconsistent prices for broadband connections, leaving customers confused and short-changed, according to research released Tuesday by the European Commission.

One study suggested European internet service providers delivered on average only 75 percent of the internet speed their customers had paid for, a gap which the Commission claimed was as wide now as it was in 2012.

Another report found prices charged for internet access varied by up to 400 percent from one EU country to the next, with users in Lithuania charged an average of 10 euros per month for a standard 12-30 megabit per second deal, and Polish users facing prices of up to 140 euros.

Among the cheaper EU countries for broadband connections were Romania and Latvia, while Spain, Ireland and Croatia were among the most expensive.

The EU's commissioner for the digital agenda, Neelie Kroes, used the findings of the four studies to claim that the EU's 400 million internet users were facing a "geographic lottery" when choosing their broadband provider.

"There is no single market for internet and that has to change," Kroes said, arguing that there was "no good reason" for one EU resident to pay 4 times more than another for the same product.

While in theory the EU's 28 member states make up a single market, internet service providers have been slow to integrate, with national industry regulation stymying attempts to allow cross-border competition.

The commissioner also attacked the industry over broadband users' lack of understanding of what they had signed up for, with one of the four studies released suggesting customers were baffled by their contracts and were making ill-informed choices.

"It is time for companies to work together to find better ways to advertise and explain their products," Kroes said in a statement.

Yet European internet service providers questioned the methodology of the research, arguing that in the countries with statistically acceptable sample sizes, the services provided were improving significantly.

European Telecommunications Network Organisation (ETNO), representing Europe's major service providers, also hit back, saying members "put continuous efforts into improving transparency and meaningfulness of the information we deliver."

ETNO also rejected the Commission's concerns over price differences across the EU, arguing they were "justified by different national market conditions and dynamics."

Commissioner Kroes has sponsored a range of new laws to create a single digital market in the EU, a legislative package called "Connected Continent" which is expected to be debated in the European Parliament in early April.

If adopted, the reforms would compel internet service providers to provide users with precise information on download speeds and would enable customers to back out of contracts if the service proved to be slower than advertised.