It's better to send resume and CV along with motivational letter. Here is a letter which might help you.
Dear Sir or Madam,
I am writing to you to apply for a summer work placement at your department.
My name is AB and I come from Finland. This semester I am studying at the University of Sheffield as an Erasmus Student. I study Human Geography programme with specialisation in regional development and regional policy. I would like to utilize the opportunity of studying in the United Kingdom and extend my stay beyond the end of the semester over summer holiday. My plan is to spend this time by work placement at a regional planning department.
I have explored your internet pages, and I was very interested in the topics you are dealing with, such as the creation of Local Plans, Joint Structure Plan or Local Development Framework. I would like to apply for a 4-week placement in June or July, most preferably at the Department of Forward Planning.
During my prior studies I have been working on several training developmental projects. We were mostly engaging with rural microregions’ strategic plans. During this projects I have learnt basics of regional planning and the creation of strategic and developmental plans. I also have a good theoretical knowledge of the European Structural Funds.
I think I could bring a lot of assets to your team. I can offer strong commitment to work. I am very reliable person who can work hard. I learn quickly and after short training I am perfectly able to work independently, but at the same time, I am a team player. I believe, I could enrich your team with my international background and perspective.
The stay in Yorkshire gave me a good opportunity to get in touch with local environment and people, and, I have to say, I really got to like the region. I am excited by the pace of the changes, it is currently going through. The opportunity to actually take part in these changes would be priceless. Furthermore, I believe, the placement would really help me in my future studies and prospective career. At the same time I believe, I could be a useful member of your team and bring a lot of positive elements into your department.
Please find my enclosed CV. Thank you for considering my request. I am looking forward to your reply.