Ladies, please clarify for me please. Are you looking for 1 stop shopping, packages, with flights, hotel and car all included? Or do you want to choose and book them yourself and aren't sure where to begin? Or possibly a travel agent that can customize a trip? Your budget may dictate to a certain extent which approach or combination may be the best for you.

England and Ireland are both big places.

Your title says 15 days - but the post says 8-9 days in each country. If you only have 15 days - then spend it all in Ireland - OR - all in England - OR - most in Ireland and a few days in London.

As for the gist of your post - not sure exactly what you are asking. You can use a travel agent to book your flights and maybe hotels in major cities. But if you have arranged your own travel anywhere else - doing so in the UK is no different and you can do it yourself.

TAs seldom are of ANY use booking B&Bs. And we here can help you more than any TA devising an itinerary.

The first thing you want to do is come up w/ at least a basic outline of an itinerary - get a couple of guidebooks if you need more info about each country.

As said, a travel agent will do most of it for you.

If you want to plan only some of it yourself there are packages availabe for a self drive itinerary. We did one in Iceland where the package included a car and accommodation for each night. It gave you a suggested itinerary for each day but what you did was up to you. We simply turned up to each hotel each evening with our voucher.

http://www.myguidebritain.com/welcome-to-myguidebritain
http://www.realbritaincompany.com/how-we-work/
Here are couple off a quick google search that will get you going.

If you want to do the whole lot your self. Start with your flights or transport into and out of the countries as these are the ones that are have the least flexibility. They set your start and finish.

Then organise transport - car or rail passes etc.

Book accommodation for your first and last nights.

Then look at where you want to go and plan a rough itinerary.
Do you want to do a "Grand Tour" or not stray too far and see a few things in detail.

If it only a short trip you should be able to book most nights as you really can't get too far in a week or so.

If you have "Must do" things that require a ticket book them as well.

If you want more flexibility the tourist information centres in England can book you into B&Bs, hotels etc. They have their favourites and will ring them and then give you directions.

For a short trip I would recommend booking most, if not all nights, as it becomes tedious getting into an unfamiliar town and then trying to find accommodation.

I suggest planing a morning activity and an afternoon activity.

Remember also, that driving in England is quite slow as there are lots of villages in the way. Most towns do not have much street parking so you will need to park in one of the multi storey carparks or similar then get out and walk.

Hope this helps and apologies if it is stating the obvious. When you said first trip. Did you mean first time to Engalnd or first time travelling out of your country? that will greatly help us with what information you need.

Do Not....sign up to any Travel Agent itinerary without running it through at least one forum..

You might just (in fact probably) be putting your holiday in the hands of someone who has been to neither or at best one of the countries.

Break this down into Two separate items...X days UK mainland, Y days Island of Ireland. These will be connected by flying from one to the other on "Regional" airlines and this will dictate the amount of Baggage.

There are Good Fly drive packages to both locations but avoid accommodation vouchers which are accepted in less than 10% of places in either country.

I don't have a lot of confidence in travel agents after my 1 experience, now years ago, booking a trip to London. The hotel she booked for me was completely inappropriate, suitable for the students and backpackers who filled the lobby but not for me. The owner made a call and sent me to a lovely place, knew immediately what I needed and responded. But the travel agent was useless as she didn't know what she was selling. And I think, sadly, it's true too often.

Agents and online sites that sell all inclusive packages are no good as a rule if you're looking for accommodations with character. An airfare/car package, as Tony mentions, can be useful if you're up to the task of finding your own accommodations which can be quite a fun process. But certainly more work as you must decide, of course, where you'll be when. There are so many charming places to stay in both countries it would be worth the work with a combination of guidebooks and websites.

Here are some accommodation sites I like:
http://www.sawdays.co.uk
https://www.airbnb.com/
http://www.athomeinlondon.co.uk/

Thanks MmePerdu for the links there is a B&B 20 min walk from where I need to be in London. Hopefully it will be vacant when I need to book.