Should we protect our technology & design in the US or in Europe?

You obviously want protection where you are truly going to commercialize the devices - patents are territorial so a US patent will not cover you in Europe and a European patent will not cover you in the US - you said that potentially, both the US and Europe are potential markets, so you obviously have a difficult choice. One option may be to file a PCT application in Europe - either in the UK or at the IB - that way you do not have to actually pursue national stage applications either in the US or the UK for 30 months - this two and one half year time span may assist you in getting needed financing to help you then pursue patents in both the US or European venues or by that time, your real market potential assessment may be clearer whereby you can clearly choose to either pursue a US patent or a European patent if you still cannot financially handle filing patent applications in both venues.

In the beginning, you will need a lot of guidance. Thus, find an experienced patent attorney who is accessible and in whom you trust. He/she will help to "capture" you invention and design in the best way, and prepare and file first filings. Thanks to the Paris Convention and international treaties, like the PCT for patent applications, subsequent filings can be filed within 6 months (for desgins) or 12 months (for inventions / patents) from the first filings.
In view of costs, it may be advisable to file national applications first and decide on subsequnet filings later on. Thus, in your situation you may start at the UKIPO or, for the design, at the EU IPO (formerly OHIM). The first filings serving as basis for the subsequent filings, should take US and EP practice into account.
'Hope this helps.
Feel free to get in touch!

With regard to the utility (technology) aspect of your invention, if you are not in a position to decide yet and want to keep your options open, you can file a PCT (patent Cooperation Treaty) application. 148 countries have signed this treaty to date, including the US and European countries. You can file the PCT application with your EU patent office. Then you have 30 months from the filing date of the international (PCT) patent application to decide in which countries to pursue protection.