Britain has financial and diplomatic weapons it can use against Russia to respond to the suspected poisoning of a former spy with a nerve agent, but it is unclear how willing the government is to wield them, or that they would influence the behavior of the Kremlin.

Prime Minister Theresa May told Parliament on Monday that her government had demanded that Russia explain the attack on the former agent, Sergei V. Skripal, and his daughter, Yulia, who remain in critical condition. Lacking a “credible response” from Moscow, she said, “I will come back to this House and set out the full range of measures we will take.”

Britain’s strongest stance against President Vladimir V. Putin’s government would involve taking action both on its own and in cooperation with its allies, diplomatic and security analysts have said.

But it is too soon to gauge how much appetite those allies have to stand up to Russia on Britain’s behalf. The Kremlin is also likely to retaliate for any measures Britain takes, and past governments have been unwilling to engage in such an escalating fight.