The UK pension legislation has changed once as a result of the March 2017 Budget. Residents of the US who move their UK pensions into a QROPS will now be subject to a 25% overseas transfer charge. However there still remains the option of using an international SIPP wherein no overseas transfer charge is levied.
The amount you can take as a lump sum is 25% of the value at the time of withdrawal. Tax treatment might depend on your local tax authority, but our understanding based on advice from our providers is that no tax will be paid on the lump sum if it derives from the SIPP in Malta. This is as a result of the double tax treaty between the two countries.