Customs and Excise will give relief of duty on aircraft parts. For this you require an end user number. The application form for this is Number C1317. Details of this is given in Customs Notice 770. the EU number is usually valid to 2 years and you have to renew it.
If you are unlucky to have parts damaged or incorrect parts returned to original country then you can reclaim the VAT using form C&E 1179. Details of this is given in Customs Notice 266.
Please check the validity of this information prior to use as there are regular updates.
To obtain information and forms go to HM Customs & Excise and search for these form numbers.
It is also worth having Van's check on cost of air freight against sea freight as some have found this to work out cheaper as well as faster.
For shipping large parts and consolidating with others contact
UK Specialist shippers. They also offer advice on shipping and customs
procedures etc.