Custom Attribute Date Type

For a project at Smart Pension we are creating an optional custom attribute as a date type, the python environment we are using is set to a timezone of UTC to match our internal data source. The custom date attribute when retrieved appears to be converted to a British Summer Time time zone. Since its being stored as a unix epoch date we have changed the type to a number which is unchanged when its retrieved.

How can we use the date type and keep the UTC time zone attribute.