The new swimming competition structure announced by British Swimming is being implemented from 2015. Details of the key summer championships are:

British Summer Championships

To be held 28th July – 2nd August 2015 at Ponds Forge, Sheffield.

The British Championships will be for swimmers aged 13yrs and over (age as at 31st December).

Qualification for these Championships will be determined by a top 24 ranking per event and per age from the British ranking list from a qualifying window of 13th March – 31st May 2015.

The event includes multi-classification events, but Para swimmers will be by invitation only (likely to be based on rankings also).
Further details are available at : http://www.swimming.org/britishswimming/calendar/british-summer-nationals-2015

The original announcement from British Swimming about the qualification period is available here.

ASA Home Nation Summer Championships

To be held 4th-9th August 2015 in Sheffield, 23rd-29th July 2015 in Swansea, 24th-26th July in Edinburgh.

The Home Nation Championships will be for English/Welsh/Scottish swimmers aged 12yrs and over (age at 31st December).

Qualification for these Championships for our swimmers will be determined from the Home Nation ranking list from the same window as the British Champs (13th March-31st May 2015) for individuals who have not qualified in that event for the British Summer Champs. Any swimmer who wishes to be ranked by their Country of International Representation (rather than by ranked club) needs to register this intent directly as instructed here.
The event includes multi-classification events, so Para swimmers can enter subject to meeting qualifying times, available on the British Swimming website.

The number of swimmers to be invited will be set by the Home Nation and there may also be some further discretion around other qualifying methods, set by the Home Nation.

Further details are available at: http://www.swimming.org/britishswimming/calendar/asa-national-championships