Question
1. I heard that there was an air borne infection that can infect ash trees even kill them, I think it was a TV news item saying the disease was bought into the country by infected trees ? My tree at the bottom of the garden is an Ash, its has a good covering of foliage and estimate its about 60-70 ft tall, there is another property behind it which is about 30 to 40ft from the nearest branch,how do I tell if my tree is healthy ? are there any marks or blemishes on the leafs or the trunk I need to check for ?

2. When the wind gets high the tree makes a lot of noise and obviously threshes with the wind, is the root spread and depth large enough to stop the tree from being toppled or blown over by high winds ? It has survived so far and I do tend to worry about it.

3. As it is very tall and does have a wide spread above ground does it need to be prooned and how much would that cost likely to be ?

Thank you for listening regards Dave

Answer
The diesease you heard about is most likely Chalara fraxinea, a deadly fungus first discovered in the UK in 2012.   It originated in Japan, and was found in Poland twenty years ago.  It has made its way to the UK, and there are over 300 confirmed sites to date.

While they are quickly working on a cure, and have made some progress based upon recent reports, there is not yet a commercially available treatment for the fungus.

See more below.

http://www.forestry.gov.uk/chalara

http://www.forestry.gov.uk/forestry/infd-8w9euv

Wind resistance depends upon a few things.

Soil conditions
Surroundings and changes to surroundings
Health or vigor of tree

A healthy tree will grow in an environment where it is able to withstand normal winds it experiences.  Trees in very windy areas will grow differently than those in sheltered areas.   If there are a lot of trees surrounding yours that have been cut down, exposing it to new wind exposure the risk will go up.

The soil is a big impact as well, some soils or if the soil is shallow over rock, or if there has been excavation then the root system may be compromised.  

Trees with health issues, a lot of deadwood, or root related issues such as root rot also impact ability to withstand winds.

Generally speaking however, a healthy tree can withstand normal winds, assuming there have been no changes in its environment.  

As for pruning, you can do some crown thinning or crown reduction if you wish.   Hire somebody who understands proper pruning techniques, and follows best practices.  Some companies, even though they are operating as tree services do not perform pruning practices that are healthy i over a long term to the tree.  Many may perform topping and call crown reduction, topping used to be performed and considered appropriate.  We have however learned that it is not healthy, and in fact increases the risk.   

http://www.treesaregood.com/treecare/topping.aspx

Another practice is lionstailing, which some will do when crown thinning.  A practice that again increases risk.  

Cost is difficult to assess, as it varies based upon many factors.

Are you wanting all brush removed?
What is access like?
How far is work from where chipping will be done?
What work will be performed, and how long will it take?   Can bucket truck get access, or is it all climbing?

By the way do not let tree service use climbers, spurs, spikes ( called by various names ) when working on tree.  It causes excess wound holes, and potential pathogen access.