Simply log into your MR account, select "Use Points" -> "...more Travel" -> "Transfer Points", find British Airways, and you will see every 1,000 MR points = 1,500 Avios.
Note that the transfer feature is only available on regular MR and MR First cards, not on MR Express cards. Confused by the level of MR cards? Check out our featured review SPG vs. MR vs. UR. We blogged about the devaluation of MR program in January and now certainly welcome Amex to come up with the new transfer offer to keep MR competitive, especially considering Chase has gained momentum with its aggressive campaign on its Ultimate Rewards program.