If I put £100,000 as working capital into a Spanish company, can this company provide £100,000 to my wife and myself as a personal loan at 6% per annum for a buy-to-let property in the UK? Can I offset the interest amount against the rental amount received from the property?

 

The company can certainly lend you the money. For the interest to be allowable against the rental income, see here that this is allowable if the rate is a commercial rate of interest, made on a normal commercial basis. There are rules for a close company lending money to a participator (see here), but a company not resident in the UK cannot be a close company for these purposes (see here). However, it is not clear to me whether this Spanish company is subject to UK corporation tax (e.g. is it centrally managed and controlled in the UK: here.