Marrow - Cucurbita pepo
There are many garden varieties and subspecies leading to quite a lot of variety in appearance. If you pick a marrow when small, it's classed as a courgette when left on the plant to grow larger it is called a marrow.
Cucurbita maxima (Pumpkin) is now grown commercially, and may naturalise. It has narrow, terete female pedicels.

Unless identified by a recognised expert, a photo is required. If the photo doesn't show the key ID features then in the comments box describe the size and identifying characters you have observed.
Rubbish tips and waste places. The majority of plants occur casually and originate from kitchen waste or from seeds of ornamental gourds.
Usually flowers between July and September.
Annual. Frequently grown as a garden crop.
Widespread records from the southern half of Britain.
Status in Leicestershire and Rutland not known.
Leicestershire & Rutland Map
Enter a town or village to see local records
MAP KEY:
Yellow squares = NBN records (all known data)
Coloured circles = NatureSpot records: 2020+ | 2015-2019 | pre-2015