Hi GordoTrek
Yes the numbers 11153 is in the same position, orientation and size of usual Holdsworth serial numbers. As you can see from Dave Scrimshaw's graphs number would date to c.1949, leaning towards 1950. FYI I have a Holdsworth sirocco # 13006 that is dated to 1951.
Do you know what model yours is? Pics of frame are always interesting and helpful with dating.
Doug