Competition watchdogs have outlined their concerns about proposals from the four supermarket rivals vying to take control of Middlesex-based Safeway in a 33-point letter.

The Competition Commission is examining whether any of the proposed deals would create an excessively dominant supermarket group which would damage shoppers and suppliers.

At the heart of the bids from Tesco, Sainsbury's, Morrison and Wal-Mart-owned Asda are local and national competition issues, prices and the impact of the potential mergers on suppliers.

But also included in the letter are issues as varied as whether the commission should consider competition for non-food sales as well as groceries, internet home shopping and the price of petrol in its inquiry.

One other consideration the letter highlighted was whether Safeway, based in Hayes, could offer effective competition to its rivals if it were left as an independent operator.

The number of issues identified for further consideration by the commission highlights the sheer complexity of the competition situation surrounding supermarkets.

A potential combination of ITV giants Carlton and Granada last month attracted a 26-point letter from the commission.