There are several native woods. Ash or elm well seasoned are the second choice. Stovie on this board has proved that hazel will work given a chance. First choice is yew but I wouldn't recommend it for a first bow.
Most of the fruit woods, holly and hawthorn if you can find straight and knot free bits with no twist, are also good but hard to find.
For non-native woods dagame and ipe are both possibles. Ipe is quite cheap if you buy it as decking.
Maple is marginal but will work for wide, thin limbs.
There is not much in the way of cordage for the string in the UK. If I want a 'primitive' string I use hemp. I wouldn't use anyting except dacron for bows over 30lbs draw because the hemp will make a very thick string. A chum of mine has successfully used linen on a 50lb bow.
Phormium, yucca and agave fibres will make a very strong cordage if you can get it.
All I do for finish is use danish oil and then a coat of silicone furniture polish. You can use boiled linseed and turps followed by beeswax if you want to be a bt more natural.