How about partitioning the workshop and heating part of it - especially for using high-vibration tools?

You can also get industrial gloves that are fingerless, helps to keep the hands warm and allows dexterity. Also, allow for a warm rest area and sufficent breaks for people who getting cold.

Do employees at least have a warm area and are they allowed to take regular breaks out of the cold environment? The Workplace regs guidance states that The temperature in workrooms should provide reasonable comfort without the need for special clothing. Where such a temperature is impractical because of hot or cold processes, all reasonable steps should be taken to achieve a temperature which is as close as possible to comfortable. ‘Workroom’ means a room where people normally work for more than short periods. I would do all you can to try and achieve a comfortable temperature using local heating if possible, especially given the use of vibrating tools and the increased risk of ill health due to reduced circulation in cold temperatures