How much is a pint of milk? A loaf of bread? A Big Mac meal? These are the sorts of questions which politicians are asked to prove that they are regular people.

In reality, of course, many prices vary dramatically depending on where you are and the place you buy a product. Some things, however, are constant.

Or so I thought.

Like many, I assumed that the price of a Big Mac meal was one of these stabile tangibles – identical food served in identical restaurants. Actually though – this may come as a shock to some readers – the price of a Big Mac meal varies from McDonald’s to McDonald’s. And not by a couple of pence, either, but dramatically, even within London .

Inspired by The Economist’s Big Mac Index, which measures the strength of a country’s currency – its buying power – by comparing the cost of a Big Mac across global cities, I determined to survey the price of a Big Mac meal on an urban scale. My theory was that this would provide an insight into economic strength across London.

Although I was certain from my own extensive pre-research that prices at McDonald’s varied, I was unsure as to how great an extent the prices would fluctuate. My assumption was that I would find two prices points that would broadly divide the city into a doughnut: either with reduced prices in the suburbs surrounding higher ones in the centre, or vice versa. My thinking was that either city centre prices are hiked up to take advantage of high footfall; or, alternatively, that outer area prices would be high, because competition for fast food was less intense.

Surprisingly, given the apparent transparency of the Internet, McDonald’s prices are not widely available. So, supported by friends and family, we set out gather the prices of regular Big Mac meals at as many McDonald’s within the confines of the M25 as possible. As of now, we’ve visited 57 of them, around 30 per cent of the total.

Variant Big Mac prices in central London. Green is cheap, dark red is pricey. Image: Tom Ravenscroft.

We soon discovered that the price of a Big Mac meal varies greatly. Within the M25, a Big Mac Meal can cost up to 60 pence more, depending on where you are.

The answer to the question I’m sure you are all asking surprised me. At £4.09 for a Big Mac meal, the affluent suburb of Greenwich was the cheapest location we found (of the McDonalds we visited in the admittedly none-too scientific survey).  

At the other end of the scale, the most expensive McDonald’s can be found in Victoria Station, Romford shopping centre and Cobham, where a Big Mac meal will set you back a whopping (oops, wrong burger chain) £4.69.

Across the city, prices vary between these two extremes. The majority of meals are priced at £4.49 and £4.59, and as a general rule if you are paying more than this, then you are paying too much. Anything less than £4.49 is good value, and if you happen to be in Greenwich then, well, stock up.

Overall, it is almost impossible to determine a board pattern or even rules. Prices do not seem to be more expensive in Zone 1 than the suburbs. While the majority of central McDonald’s are priced at £4.49 and £4.59 many others are not: Baker Street for example is £4.39. And while Peckham and Kingston Big Mac meals are cheap at £4.39, Forest Gate and Southall are £4.59 and at Romford they are charging £4.69.

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Varying prices around Victoria: darker is pricier. Image: Tom Ravenscroft.

On a micro scale, prices also vary greatly within very small distances. The three McDonald’s in and around Victoria Station, for example, all sell Big Mac meals at different prices. Within the station itself walking 300 metres to the upstairs restaurant will save you 20p. Walking from Warren Street to Camden will save you 40p.

One might assume that this is due to the exact locale of a restaurant: perhaps restaurants within a shopping centre or station would be cheaper than those on a high street. This holds true at Paddington where there is a there is a 10p premium for eating in the station, compared to the restaurant just outside. However, at £4.39 the McDonald’s in Waterloo is one of the cheapest in central London, and at Victoria, the restaurant in the station food court is 10p cheaper that the restaurant outside the station.

Surprising variations around the Euston Road. Image: Tom Ravenscroft.

The results of the survey have proved two things. Firstly, that, while the rise of the internet has greatly improved price transparency, the prices of some services are still largely unkown. Secondly, it shows that cities are extremely complex places, where numerous factors determine how a chain likes McDonald’s sets its prices.

Of course the size of my appetite meant I was only working with a small sample. More information would undoubtedly give better results and I am continuing the survey – you can contribute here.

View the full results on an interactive map here. 

Tom Ravenscroft is an architectural historian  and the editor of BIM+. He tweets as @tomravenscroft.