Working for a uk company from home or in rented office - Portugal tax/ working laws

I am a resident in Albufeira but work for a LTD company in the UK, no sales revenues are received/conducted in Portugal, US based and UK websites provide company revenues. I work daily from home in Portugal via the Internet, answering emails, skype conferencing, technical support for US based customers and writing software etc. I never perform transactions of any kind on Portugese soil. I am simply in Portugal to enjoy cheaper living costs and the weather - but I have to continue with most of the work duties i would be doing on UK soil. My tax is handled and paid as normal within the UK via my company/employers. On a monthly basis i transfer some living expenses to Barclays in Portugal and use that to pay rent in Euros etc Due to the need to have a stable working environment - I was considering renting an office in Albufeira to work from to avoid interuptions at home which can be frequent enough to warrant the added cost of a dedicated working space. I am wondering what implications there are for Tax or working laws with the Portugese authorities for both scenarios, working from a home based office or renting an office space. many thanks Tom