I was standing on a rooftop in central London on the last day of filming a crucial scene for Sherlock when I got a call offering me the role of production designer on the new series of Upstairs Downstairs BUT - I had to start the following day!

This was my introduction to the rollercoaster ride that was to take over my life for the next five months.

We pick up the story of 165 Eaton Place in September 1938 which is a great era for design - the height of art deco.

In order to see this content you need to have both Javascript enabled and Flash installed. Visit BBC Webwise for full instructions

Returning to 165 Eaton Place

As the production designer, I was very keen to utilise this in our distinction between 'Upstairs' and 'Downstairs' - the opulence and crisp elegant lines of art deco as opposed to the rougher, more textured world of the working classes.

The interior of the house is all a set and is spread between three studios at BBC Wales' new facility down in Cardiff Bay (next door to Casualty and Pobol y Cwm).

We've added a couple of extra rooms to the interior set this year and one of those is a dining room.

I enjoyed designing it as we were able to introduce some very contemporary shapes and patterns into the set. Look out for the pair of doors leading into the dining room and the floor inside.

We designed and made these ourselves - without seeming too Changing Rooms, they're all paint effect and MDF!!

The main hall is in a larger studio than the rest to allow for it to be two storeys, which helps sell the idea of it being a real house. You can follow the actors from the dining room across the hall and up the stairs to the landing and drawing room.

The decorating of these sets correctly is very important.

We must make sure that the patterns and colours look good on camera, so we co-ordinate with the costume department to make sure that the actors' outfits are complementary to the scenery and don't blend into the background.

The cost of redecorating a room could be the difference between coming in on or over budget.

Therefore I have to discuss options and themes beforehand - with the producer, director, director of photography and costume. I have to admit that I tend to get my own way most of the time!

Harry Spargo (Neil Jackson) and one of the vintage cars

Interior design is only one aspect of the job however, and as much as I like my wallpapers, we also have cars, planes, trains and buses to source as well as all the props.

I have a very good team helping me with all these as it would be an impossible task on your own - the organising of the vehicles alone is a monumental task.

The cars, for example, are mostly privately owned and are brought to set by the owners or drivers on their behalf. Due to their age some are trailered if they need to travel very far.

The aeroplane we sourced from Duxford Air Museum, who were, as always, very helpful.

It's also a big task sourcing the dressing props (what we use to make the sets look real) and action props, which are used by the actors and often described in the script which means we have to source or reproduce. We hire some, trawl round antiques markets for others, and eBay is also a good resource.

We even have some made especially - look for the special gasproof pram! It was based on a real one but there were only a few very sketchy photos that survive of it, which were sourced from the internet and some old newsreel.

Downstairs: Anne Reid as Mrs Thackeray

There is also all the food and flowers. The end products of Mrs Thackeray 's work in the kitchen need to both look good enough to serve at a royal dinner party and be authentic for the period.

Because of this a specialist TV and film food economist was hired in.

She would pre-prepare some of the food and then it would be finished in a specially-made food preparation area just outside the studio so that we could serve it piping hot straight to set!

To support her expert work, we also depended on the culinary skills of our very own Hannah Nicholson (my set decorator) who also did most of the flower arranging as well as a myriad of other things!

It was a very challenging project but with a great team behind me I think we managed to achieve something beautiful - I hope you agree.

Arwel Wyn Jones is the production designer on Upstairs Downstairs.

Upstairs Downstairs returns to BBC One and BBC One HD on Sunday, 19 February at 9.30pm. For further programme times, please see the episode guide.

Comments made by writers on the BBC TV blog are their own opinions and not necessarily those of the BBC.