MOSCOW — The loyalist that President Putin has chosen to succeed him accused the British Council of espionage yesterday, denting hopes of a swift resolution to the diplomatic crisis between Russia and Britain.

Dmitry Medvedev, who is poised to be anointed as president when Russia goes to the polls next month, said he backed the decision to close the British Council’s offices in St. Petersburg and Yekaterinburg. Blaming periodic rows with London on Britain’s historic desire to be “mistress of the seas,” Mr. Medvedev repeated the claims of Kremlin hard-liners that the council provided cover to secret agents.

“If someone allows you in their home, act decently,” he was quoted as saying in the weekly Itogi newspaper.

“After all, it is known that state-financed structures like the British Council conduct a mass of other activities that are not so widely publicized.

“Among other things, they are involved in gathering information and conducting espionage activities.”

Mr. Medvedev’s comments are likely to heighten fears that Russia’s next leader will pursue Mr. Putin’s aggressive policies toward the West.

Until now, the first deputy prime minister has portrayed himself as a moderate and has avoided directly addressing many of Russia’s most controversial disputes with ex-Soviet neighbors and the West. British diplomats concede that a change in presidency is now unlikely to end the council’s woes. Unlike his predecessor and many of his Kremlin colleagues, Mr. Medvedev is not a former KGB spy. Even so, he has promised to follow Mr. Putin’s policies. With genuine Kremlin critics barred from contesting the election, Mr. Medvedev is expected to win by a landslide.