Suggest you pick a couple of points from here -
http://www.wikijob.co.uk/wiki/why-do-you-want-work-small-firm
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People at smaller companies may make less money and enjoy fewer perks than their big city counterparts, but they are much more likely than big-company employees to describe themselves as "extremely satisfied" with their jobs. One advantage in small firms is the increased recognition from managers, and the increased team spirit that is often not part of working life at large companies.
Smaller firms tend to be more supportive, less bureaucratic and more willing to hire workers embarking on new careers. If you are the kind of person who has ideas and can come up with new ways of doing things, it is much more likely that a small company will listen to you and take your ideas on board. At a large company, just finding out who to suggest ideas to can be a hassle, let alone scheduling a meeting to talk about them.
In small companies, people know about each other much more intimately. Whilst this means that news of a work-based romance may spread across your office within a few hours, it also means that your hard work and good ideas are likely to receive the recognition they deserve. Work particularly hard or have a fantastic idea in a small company and the owner is likely to find out about it by the end of the week. In a large company, you might never even meet the owner or any senior staff at all.
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