Henley & Partners said its volume of engagement with clients seeking alternative citizenship or residence by investment climbed 40% in the first quarter of 2020 versus Q1 2019, before flattening during the COVID-19 lockdown in Q2.
But interest has rallied since July 1, with a 15% year-on-year increase in engagement to Sept. 10, as the end of the Brexit transition phase nears.
Henley & Partners' Blewer said clients were increasingly drawn to Caribbean citizenship applications - which is likely to give them better travel access to the EU than Britain - but which have a lower minimum investment and a quicker approval process.
Saint Lucia citizenship, offering visa-free travel to 146 countries, can be obtained in around four months for a minimum investment of 76,152 pounds, data supplied by Astons showed.
For less than 40,000 pounds more, investors can obtain citizenship of St. Kitts & Nevis - and visa-free travel to 156 countries - in around 60 days.
In contrast, Malta offers citizenship in exchange for around 1 million pounds of investment, but the process takes up to 14 months.
Portugal, meanwhile, typically processes investment migration applications in three months but only grants EU residency to investors and visa-fee travel to just 26 countries.
"With HNWIs, time is often more important than what is essentially a small fluctuation in cost and many are looking to secure additional citizenship as fast as possible in the pandemic landscape," Arthur Sarkisian, managing director of Astons, said.
EU authorities are under pressure to clamp down on investment migration programmes by member states.
Sven Giegold, a member of the European Parliament from Germany's Green party, said these kind of citizenship sales "posed a serious threat to EU security and the fight against corruption" in the bloc.
"EU passports and visas are not a commodity. Money must not be the criterion for citizenship and residence rights in the EU," he said.