Pucklechurch services would have been located on the M4 between J18 and J19, about half way between Leigh Delamere and Aust. It has all four ghost slips, but the land hasn't been prepared for the services.
Either side, the road is served by a farm access road, which would have probably served as the services's 'secret exit'. This would suggest that the plans were in the pipeline when the M4 was first planned.
Ghost Slips - Other Uses
In the 1960s there were talks about the Bristol East Loop Road meeting the M4 at a new junction "near Pucklechurch, close to J18", but this was ruled out. It's not unheard of for planned service area sites to have been considered for other uses too.
The ghost slips have been used to store machines relating to the roadworks in this area.
In 1986 Granada submitted a plan to build a service area at this exact location. Their plan would have used curved sliproads meaning the ghost slips would have had to be removed, which meant the services would have to be mounted vertically instead of horizontally (the end result being that not all of the site originally reserved for the services was used, but the site spilled into nearby fields).
This kept the amenities building as far from the road as possible, allowing for a better break, and less interference with the motorway. Briefly during the planning process there were plans for a fourth lane on the M4, which meant a gap was left in the plans.
There would have been parking for 238 cars and a Granada Lodge on the westbound side. The two secret exits would have formed staff car parks, but they wouldn't have been connected to the service area itself, owing to local objections.
The plans were dropped following concerns about it being a green belt area, and because Leigh Delamere was too close nearby. The case dragged on over 13 years and attracted two rival bids from Total, one of which incorporated the proposed J18a.