General trends in uk trade last 30 years?

Unfortunately, that information is not readily available online. Information can be found for the most current years regarding the statistics in general trade. For 30 years of data, you will need to locate the information in written format. You may try to locate the information at your local library.
Libraries often have access to past information regarding a country. It is possible they will have UK trade books that will show you the information you seek for the last 30 years of UK trade.
Since it is general trade, it makes it more difficult to answer this question. Most online sites break down trade per industry and then determine the statistics for the most recent years.
If you are talking about general stock trading statistics, you may be able to obtain graphs and all other information by belonging to an online trade site such as:

• OptionsXpress
• Optionshouse
• TradeKing
• Scottrade

These stock trading sites will provide you with access to data that is not available anywhere else, except in a library or government building. Stock trading sites will look at various different stocks. These can include some general trade topics. You may not be able to go back 30 years, but you will have access to more data than any other site online from what could be found.
A lot of company data will also showcase the past and is determined by how much the company is willing to share. You may find the data you seek based on the above information. There may also be some written reports you can find through a university library to provide you with the necessary UK trade information you seek.