The BoE said it would temporarily buy long-dated bonds - linked most closely to workers' pensions and home loans - in light of a surge in 30-year UK bond yields above 5%, their highest since 2002.
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"The surge in bond yields threatens the housing market and broader economy.
Wall Street opened higher, with the S&P 500 Index (.SPX) up about 1% after it fell to a two year low on Tuesday.
Scott Wren, Senior Global Market Strategist at Wells Fargo Investment Institute, said markets may already be pricing in future pain.