Watching archaeologists at work on construction sites in London over the years, I’ve often wondered what happens to all the artefacts they unearth. The major finds often soon end up on show to the public in special museum exhibitions, but what about the mere fragments that – to the untrained eye – don’t seem interesting?

That very question was answered at the weekend as I was given a tour of the Museum of London Archaeological Archive, housed in a cavernous former steel factory in Hackney. According to a plaque from the Guinness World of records on the wall it is the largest archaeological archive in the world, with an estimated 120,000 shoe-sized boxes stacked on some 12km of shelving. It’s very telling that there are just a few containers from 1991 when there was a recession on.

Unfortunately I wasn’t allowed to take any photos inside, so some imagination will be required here. But when I entered I was reminded of a giant Amazon warehouse that I had recently seen on the television recently, where the locations of all the goods was carefully recorded. Web order pickers, like archaeologists, need to know quickly where particular items can be found.

Much as books and CDs are often loved by their owners, the items in this store are deemed much more precious. Artefacts date from pre-history right through to Victorian times (more modern items, like recent mobile phone models, are collected in the social history centre downstairs). The store contains everything from Roman shoes to a pair of 200-year-old false teeth.

And although I was given a tour of the whole of the upper floor archives, the main theme of the day was Roman Britain. The objects that the enthusiastic volunteers showed our group were largely from two villas excavated on the fringes of London. We were shown a range of artefacts including pieces mosaic flooring, dice and animal skulls.

Preservation techniques at the archives have changed over the years and since 2001 there has been a major project to re-package every single item in store. This involves painstakingly removing artefacts from their plastic bags and putting them in new ones that have holes in them, so they are breathable.

I had a go at this re-packaging exercise during my tour of the archives and got a sense of how precise this task needs to be. The clear bags needed to folded, stapled and have special index cards (which are expected to last for around one hundred years) inserted in very particular ways. It’s a huge job and one that volunteers can help with as part of a special community engagement programme (a new intake is apparently due to start in April).

What surprised me was that even the smallest fragments often have their own label and bag. I re-packaged a stone fragment that wasn’t much bigger than a postage stamp. Wouldn’t it be easier if a number of similar-sized pieces were grouped together? Apparently not – ‘context’ is key here. If the artefacts weren’t found in exactly the same spot on a site, they can’t go in the same bag.

And while re-packaging London’s past is already a massive undertaking, staff and volunteers at the centre face the challenge of new discoveries coming in by the day. The massive Crossrail building programme is unearthing considerable archaeological finds. Many of these artefacts will never be seen by the general public because they just aren’t interesting enough, but to the trained eye when different bits are pieced together like a jigsaw they create a valuable picture of London’s past.

The fact that archaeology in the UK – and particularly London – is enjoying such a renaissance at the moment is largely thanks to new rules introduced in 1992 that make digs compulsory before new buildings are constructed in areas deemed to have the possibility of significant history buried ground. Given the number of building projects taking place in London at the moment, a number of digs have taken place in recent years.

Developers must pay for an organisation like the Museum of London Archaeology Organisation (MOLA) – now a commercial arm whose work stretches beyond the capital – to launch an exploratory dig before a single brick is laid. This process of course often requires a considerable amount of negotiation.

On one side, the land owners usually want to get moving with construction so they can get tenants in as soon as possible. And of course they are picking up the bill for the dig. On the other, archaeologists want to embark on a comprehensive dig that will not only preserve artefacts from the past, but also ensure help with the interpretation of history.

I thought this relationship would always be tense, but volunteers I met at the weekend told me that it can actually be extremely fruitful. Developers often want to use archaeology to help engage with communities in an extremely positive way.

If building boom in the City continues and consequently archaeological digs continues at this pace, you can only imagine that the Museum of London Archaeological Archive in going to continue to be a busy place for some time yet.

To arrange a visit, see here for more information.