I will be driving over from the UK to Carvoeiro in January, towing a small trailer (Under 750k). Can any one tell me the current laws in Portugal related to towing a small trailer, ie speed limits etc.

The Portuguese equivalent to the DVLA is the DGV and information regarding legal speed limits can be found on this link:
http://www.dgv.pt/seg_rodo/lim_velocidade_ing.asp
Hope this helps.

Sorry, forgot to add this from the DGV website:
Article 110
Trailers
1. A trailer is a vehicle towed to a motor vehicle.
2. A semi-trailer is a vehicle towed to a motor vehicle which front part lays on the
motor vehicle and shares its weight on it.
3. The vehicles stated in the previous numbers are described as agricultural or forest
trailers or semi-trailers when towed to a farm tractor or to a cultivator machines.
4. Farm and forest towed machines are made for farm and forest tasks and can only
use the public way when towed.
5. A towed industrial machine is made to do industrial jobs and can only circulate in
the public way when towed.
6. Only one trailer is allowed be towed to a motor propelled vehicle.
7. Coaches or buses are not allowed to have trailers.
8. There is an exception to what is mentioned in N. 6 and 7 for using a trailer to
transport luggage in coaches, buses, tourist trains, and farm or forest tractors.
9. Anyone who disrespects what is prescribed in N.6 and 7 must pay a fine that ranges
from 120 to 600 euros.